BU-403: Charging Lead Acid

Learn how to optimize charging conditions to extend service life.

The lead acid battery uses the constant current constant voltage (CC/CV) charge method. A regulated current raises the terminal voltage until the upper charge voltage limit is reached, at which point the current drops due to saturation. The charge time is 12–16 hours and up to 36–48 hours for large stationary batteries. With higher charge currents and multi-stage charge methods, the charge time can be reduced to 8–10 hours; however, without full topping charge. Lead acid is sluggish and cannot be charged as quickly as other battery systems. (See BU-202: New Lead Acid Systems.)

Lead acid batteries should be charged in three stages, which are [1] constant-current charge, [2] topping charge and [3] float charge. The constant-current charge applies the bulk of the charge and takes up roughly half of the required charge time; the topping charge continues at a lower charge current and provides saturation, and the float charge compensates for the loss caused by self-discharge.

During the constant-current charge, the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If continually deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge. Figure 1 illustrates these three stages.

Charge stages of a lead acid battery
Figure 1: Charge stages of a lead acid battery.
The battery is fully charged when the current drops to a set low level. The float voltage is reduced.  Float charge compensates for self-discharge that all batteries exhibit.
Courtesy of Cadex

The switch from Stage 1 to 2 occurs seamlessly and happens when the battery reaches the set voltage limit. The current begins to drop as the battery starts to saturate; full charge is reached when the current decreases to 3–5 percent of the Ah rating. A battery with high leakage may never attain this low saturation current, and a plateau timer takes over to end the charge.

The correct setting of the charge voltage limit is critical and ranges from 2.30V to 2.45V per cell. Setting the voltage threshold is a compromise and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, over-saturation by not switching to float charge causes grid corrosion on the positive plate. This also leads to gassing and water-loss.

Temperature changes the voltage and this makes “dancing on the head of a needle” more difficult. A warmer ambient requires a slightly lower voltage threshold and a colder temperature prefers a higher setting. Chargers exposed to temperature fluctuations include temperature sensors to adjust the charge voltage for optimum charge efficiency.

The charge temperature coefficient of a lead acid cell is –3mV/°C. Establishing 25°C (77°F) as the midpoint, the charge voltage should be reduced by 3mV per cell for every degree above 25°C and increased by 3mV per cell for every degree below 25°C. If this is not possible, it is better to choose a lower voltage for safety reasons. Table 2 compares the advantages and limitations of various peak voltage settings.



2.30V to 2.35V/cell

2.40V to 2.45V/cell


Maximum service life; battery stays cool; charge temperature can exceed 30°C (86°F).

Higher and more consistent capacity readings; less sulfation.


Slow charge time; capacity readings may be inconsistent and declining with each cycle. Sulfation may occur without equalizing charge.

Subject to corrosion and gassing. Needs water refill. Not suitable for charging at high room temperatures, causing severe overcharge.

Table 2: Effects of charge voltage on a small lead acid battery.
Cylindrical lead acid cells have higher voltage settings than VRLA and starter batteries.

Once fully charged through saturation, the battery should not dwell at the topping voltage for more than 48 hours and must be reduced to the float voltage level. This is especially critical for sealed systems because they are less tolerant to overcharge than the flooded type. Charging beyond the specified limits turns redundant energy into heat and the battery begins to gas.

The recommended float voltage of most flooded lead acid batteries is 2.25V to 2.27V/cell. Large stationary batteries at 25°C (77°F) typically float at 2.25V/cell. Manufacturers recommend lowering the float charge when the ambient temperature rises above 29°C (85°F).

Not all chargers feature float charge and very few road vehicles have this provision. If your charger stays on topping charge and does not drop below 2.30V/cell, remove the charge after 48 hours of charging. Recharge every 6 months while in storage; AGM every 6–12 months.

These described voltage settings apply to flooded cells and batteries with a pressure relief valve of about 34kPa (5psi). Cylindrical sealed lead acid, such as the Hawker Cyclon cell, requires higher voltage settings and the limits should be set to manufacturer’s specifications. Failing to apply the recommended voltage will cause a gradual decrease in capacity due to sulfation. The Hawker Cyclon cell has a pressure relief setting of 345kPa (50psi). This allows some recombination of the gases generated during charge.

Aging batteries pose a challenge when setting the float charge voltage because each cell has its own unique condition. Connected in a string, all cells receive the same charge current and controlling individual cell voltages as each reaches full capacity is almost impossible. Weak cells may go into overcharge while strong cells remain in a starved state. A float current that is too high for the faded cell might sulfate the strong neighbor due to undercharge. Cell-balancing devices are available compensate for the differences in voltages caused by cell imbalance.

Ripple voltage also causes a problem with large stationary batteries. A voltage peak constitutes an overcharge, causing hydrogen evolution, while the valley induces a brief discharge that creates a starved state resulting in electrolyte depletion. Manufacturers limit the ripple on the charge voltage to 5 percent.

Much has been said about pulse charging of lead acid batteries to reduce sulfation. The results are inconclusive and manufacturers as well as service technicians are divided on the benefit. If sulfation could be measured and the right amount of pulsing applied, then the remedy could be beneficial; however giving a cure without knowing the underlying side effects can be harmful to the battery.

Most stationary batteries are kept on float charge and this works reasonably well. Another method is the hysteresis charge that disconnects the float current when the battery goes to standby mode. The battery is essentially put in storage and is only “borrowed” from time to time to apply a topping-charge to replenish lost energy due to self-discharge, or when a load is applied. This mode works well for installations that do not draw a load when on standby.

Lead acid batteries must always be stored in a charged state. A topping charge should be applied every 6 months to prevent the voltage from dropping below 2.05V/cell and causing the battery to sulfate. With AGM, these requirements can be relaxed.

Measuring the open circuit voltage (OCV) while in storage provides a reliable indication as to the state-of-charge of the battery. A cell voltage of 2.10V at room temperature reveals a charge of about 90 percent. Such a battery is in good condition and needs only a brief full charge prior to use. (See also BU-903: How to Measure State-of-charge.)

Observe the storage temperature when measuring the open circuit voltage. A cool battery lowers the voltage slightly and a warm one increases it. Using OCV to estimate state-of-charge works best when the battery has rested for a few hours, because a charge or discharge agitates the battery and distorts the voltage.

Some buyers do not accept shipments of new batteries if the OCV at incoming inspection is below 2.10V per cell. A low voltage suggests a partial charge due to long storage or a high self-discharge caused by a micro-short. Battery users have found that a pack arriving at a lower than specified voltage has a higher failure rate than those with higher voltages. Although in-house service can often bring such batteries to full performance, the time and equipment required adds to operational costs. (Note that the 2.10V/cell acceptance threshold does not apply to all lead acid types equally.)


Watering is the single most important step in maintaining a flooded lead acid battery; a requirement that is all too often neglected. The frequency of watering depends on usage, charge method and operating temperature. Over-charging also leads to water consumption.

A new battery should be checked every few weeks to estimate the watering requirement. This assures that the top of the plates are never exposed. A naked plate will sustain irreversible damage through oxidation, leading to reduced capacity and lower performance.

If low on electrolyte, immediately fill the battery with distilled or de-ionized water. Tap water may be acceptable in some regions. Do not fill to the correct level before charging as this could cause an overflow during charging. Always top up to the desired level after charging. Never add electrolyte as this would upset the specific gravity and promote corrosion. Watering systems eliminate low electrolyte levels by automatically adding the right amount of water.

Simple Guidelines for Charging Lead Acid Batteries

Last updated 2016-05-17

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On October 15, 2010 at 3:29am
Ted Exley wrote:

I have a 12 V AGM VRLA Sealed 28Amp Hour Battery, by Power Bat Co Inc. which I use on a golf trolley.  I charge it with a charger which appears to give a charge of 14.6 volts. A couple of hours after charge, the battery gives a voltage reading of 13.5. Charger also has a Float Charge. I usually leave the battrey on Float between rounds of golf ( 2 -3 days)

After using for 9 holes of golf, the power appears to go, yet the battery still shows a charge of 13.1 V across the terminals.  It appears to quickly re-charge again.

Any ideas of what may be wrong

On December 9, 2010 at 8:55am
ayub wrote:

nicely done, very informative.
thanks a lot.

On December 15, 2010 at 7:41am
bernard anderson wrote:

please can someone tell me why my golf battery shows 12-13 v when charged but the AH is showing 5.24 i have two batteries and they are the same readings batteries are one year old.
when i put the batteries on the trolley this drains the battery very fast. cable and motor are ok
also what does the AH stand for.
thanks for your help

On December 20, 2010 at 11:19pm
Dan Davenport wrote:

Bernard. The AH stands for Ampere Hour and is the capacity of the battery. Your batteries can supply 5.24 Amps of current for one hour duration or 1 Amp for 5.24 hours. Voltage and capacity are not the same thing. As stated above, a fully charged 6 cell battery shows about 12.65 Volts when fully charged whether it is a small car battery or a massive forklift truck battery.

If your golf trolley is discharging your batteries when not being used, you must have a short circuit or partial short in the speed controller or wiring. If they discharge too quick during use only, it sounds like they are too small a capacity for the job. 5.24 AH is pretty small to run a trolley motor. Old batteries loose capacity but yours should be in good condition being only one year old. Have you left them discharged for a long period in the garage? Lead acid batteries must always be stored in a fully charged state and be periodically recharged even when not in use. Leaving them discharged is a sure fire way to ruin them.

Hope this helps.
Dan. Laluna Technology.

On December 24, 2010 at 2:15pm
Hesham Mohamed Homam Al Hashemy wrote:

Dear Sir,

I would like to ask you two questions regarding the process of charging sealed lead acid batteries, i would be so grateful for you for taking in consideration a simple answer as i am so far from the technology of batteries.
Thanks in advance for your care and co-operation.

1)- I bought 2 new 6v 10Ah sealed lead acid batteries to use instead of the dead ones in my child’s ride-on, i also bought a simple wall charger which states that it charges at 1Ah, does this mean that to charge them for the 1st time i should leave them connected to the mains for 10 hours?
2)- I also have a 12v 1.5Ah charger, can i connect those 2 new 6v 10Ah batteries in series and charge them together and how much time would they take to be fully charged.

Best regards

On December 24, 2010 at 6:23pm
kenet kho tan wrote:

sir, i need to charge 10 6 volts batteries all at a time. what charger will i use and how fast will the batteries gets full, cause i need to use it all day long for my motorized toy car. i have 20 batteries but it drain easily when i charge it with a normal charger. thanks

On December 28, 2010 at 1:05pm
todd anderson wrote:

I have 2 8D batteries in my motorhome. I get about 10 hours use before I need to recharge. It seems to take forever (10 hours) to recharge them with the generator and 6 amp charger. After reading your article, it sounds like I shouldn’t discharge them all the way. Any suggestions for use and charging them faster?

On January 8, 2011 at 12:29pm
Vlad Leho wrote:

A question.  I need to charge three 7.5 AH 12-volt batteries for use in case of extended power failure to my Verizon FIOS phone system, whose battery will only work for 8 hours. Can I use one charger of 1000 mAh output to charge all 3 batteries in parallel and then keep them on a maintenance charge till neded?  Or will I need to charge them one at a time.  Thanks.

On January 12, 2011 at 9:23am
Carl wrote:

In a solar / wind charging system the charging circuit will manage the charging process.

What I need to know is for every 100watts of solar / wind power, how many Amp-hours of battery capacity can I add to the system?

An equaision, rule of thumb, or Max. Min. Optimum values would be most helpful.

On January 12, 2011 at 3:57pm
Carl wrote:

My Solution:

Lead-acid battery charge in 12-16 hours (10 hours with multi-stage methods, 36 hours for larger capacity batteries)

Charging voltage is critical and range from 2.30-2.45 volts per cell

Ah / hours = Amps

To charge a 100Ah battery in 12 hours I need 8.3Amps (recommended)
To charge a 100Ah battery in 16 hours I need 6.25Amps (recommended)

Charging voltage per cell x number of cells = charging voltage

Charging a 6 cell 12V battery at 2.45 volts per cell is 14.7volts max

Watts / charging voltage = Amps

A 400 Watt wind turbine makes 27.2 Amps at 14.7 Volts

Amps x hours = Ah

A 27.7A turbine can charge a 272Ah capacity in 10 hours (multi-stage required)
A 27.7A turbine can charge a 326Ah capacity in 12 hours (recommended)
A 27.7A turbine can charge a 443Ah capacity in 16 hours (recommended)
A 27.7A turbine can charge a 979Ah capacity in 36 hours (large capacity bat.)

For a 24 hour period a capacity ranging between 326Ah and 653Ah is required

A 27.2A wind turbine can charge a 326Ah battery capacity in 12 hours
A 27.2A wind turbine can charge a 653Ah battery capacity in 24 hours

All calculations are theoretical

On January 12, 2011 at 10:57pm
Girish.K wrote:

how to calculate connected load of battery chargers
360V-150A with 80% efficiency

On January 15, 2011 at 8:50am
Gerrion wrote:

Is a very useful page

On January 17, 2011 at 9:22am
Steve wrote:

More of a question:  Is it possible for a 6 volt charger to charge a automobile 12 volt lead acid battery to the point where it will have enough energy to start a car?

On January 20, 2011 at 6:32pm
Steve wrote:

younas - Not sure that I understand your response.

On January 21, 2011 at 5:00pm
catherine wrote:

I have 8 batteries 6v of 415AH. My charge controller goes to 20aac maximum ! Is it safe to charge my batteries at 20 aac up to the absorb point 28.0V

On January 21, 2011 at 6:27pm
Steve wrote:

I don’t think this answers my question.

Is it possible for a 6 volt charger to charge a automobile 12 volt lead acid battery to the point where it will have enough energy to start a car?

On January 22, 2011 at 9:59pm
Vasuki Rao wrote:

Can i use Sealed maintenance free batteries instead of Electrolyte filled ( Distilled water recharge )lead acid batteries.
My Lead acid battery is rated 75Amps, 105 minutes

On January 24, 2011 at 4:05pm
cornflake wrote:

>Is it possible for a 6 volt charger to charge a automobile 12 volt lead acid battery to the >point where it will have enough energy to start a car?

IF your car can turn over with 6V going in, sure…. It probably can’t though.  It’s not good for the battery if that battery is of any use at all.

Let’s just say no….

On January 27, 2011 at 4:24am
Gonzalo P wrote:

I have some questions I hope you can help me.

For connecting the battery as a buffer I just nead to conect in parallel the battery with my device and the charger? If the current I am taking is constant is imposible to do this, because my charger will never be able to charge the battery? Is this how the lights with backup work?

In my case my battery is a 12V 7.5A
My device use 12V 0.2A
The charger I was thinking i buying is a 4step of MASCOT - http://www.mascot.no/admin/common/getimg.asp?FileID=1350.
(This because i need that the charger works with 24V as input)


On January 28, 2011 at 9:17am
Juma Ali wrote:

how many 12v 7AH sealed lead acid rechargeable batteries should i use to watch a 62 watts 240V colour TV for 10 hours

On January 29, 2011 at 1:17am
Tajammul wrote:

I have a two year old car battery which gives enough power to start my car when cold , but it refuses to crank the engine after the car runs for more than 10 kms. It immediately jump starts.It will however start again after a rest of about 1 hour without any external help

On January 30, 2011 at 6:14am
alexander wrote:

hello everyone..well i have a banner 12v 55ah battery on my 2001 vw.the battery is 8 months old and i notice that its cant hold the proper voltage.even if i travel for a couple of hours or sort trip the battery after 3 to 4 hours from 12.6v drops to 12v..sometimes 11.8 measured with multimeter.the strange thing is that the car starts ok,litle hard know because of winter with outside temperature 10 deg C.i cant understand so help me out if u can..how can i know if my battery is fully charge or needs a simple charge…or in worse,the battery goes to die and needs replacement?
thanx for your time to read my issue..first time i meet a battery with her own personality.. smile

On January 31, 2011 at 2:22am
Anatoly wrote:

Hello everyone. Be so kind to explain meaning of treatment charge for a battery.

On January 31, 2011 at 4:27am
alexander wrote:

Accept my opologize but i cant understand the meaning of treatment charge..im from greece and my english is at low level..from litle that i can imagine that you meen im charging the battery from the alternator which produse 12v 90A standard bosch car alternator..i have to tell you also that when i start the car running im seen from the multimeter 14.4v a couple of minutes after that at idle the voltage drops at 13.7v stable..all the measuses i taked was with no extra loads..A/C, headlights on, radio etc…. thanx for your time!!
i appreciate

On February 1, 2011 at 9:38pm
Vijay Moongilan wrote:

Please help me about How to calculate AH of 12V, 65AH & 12V, 7AH lead acid batteries are connected in series?

On February 2, 2011 at 11:45am
John Cocula wrote:

I have an 12V, 8AH SLA battery that I want to test.  I have a battery tester from Harbor Freight that has a gauge for reading voltage under load, but the load it provides is definitely too much (100 amps) for my battery.  (I also have a digital multimeter.) What ampere load should I put a fully charged 12V 8AH battery under when reading its voltage, for how long, and what are examples of 12-volt DC devices that could draw that amount of current?  Extremely grateful for experienced feedback!  - John

On February 3, 2011 at 2:16am
Gonzalo P wrote:

Buying the charger is starting to be really hard, because the don’t sell just one. My problem is that for charging the battery of 12V and 7.5Ah i need to use a 24V as supply. I want to know what would happened if I just connect a DC/DC to the battery converting the 24 to 13.9V, Float charge voltage. Is this voltage able to charge the battery? I don’t have problem if charging takes a lot of time?

Thanks again!!

On February 5, 2011 at 9:42pm
abhishek pandey wrote:

    Dear Sir what type of battery charging

On February 13, 2011 at 8:35pm
James Christian wrote:

I’ve been studying this topic quite a bit recently and I would like to take a shot at answering some questions (there are lots of questions here and very few answers):

> How many 12v 7AH sealed lead acid rechargeable batteries should i use to watch a 62 watts 240V colour TV for 10 hours?

ANSWER: I have been interested in these kinds of calculations myself.  Let’s see how I do.  My inverter is rated at about 90% efficiency so I will assume this here.  Also, I will always round up to be more conservative:
A) 62 Watts / 0.90 = 69 Watts DC (amount needed going into the inverter per hour in order to provide 62 Watts AC)
B) 69 Watts x 10 hours = 690 Watts DC
C) 690 / 12 Volts = 58 Amp Hours
D) 58 Ah / 7Ah (per battery) = 9 batteries (at 7 Ah each)

> Please help me about How to calculate AH of 12V, 65AH & 12V, 7AH lead acid batteries are connected in series?

ANSWER: If you connect two twelve volt batteries in series then you will get 24 Volts; however, everything I have read is that you should NEVER connect in parallel or series two batteries of differing capacities.  It could be done once, but I think it would wear out one or both of the batteries quickly over time.

> A question.  I need to charge three 7.5 AH 12-volt batteries for use in case of extended power failure to my Verizon FIOS phone system, whose battery will only work for 8 hours. Can I use one charger of 1000 mAh output to charge all 3 batteries in parallel and then keep them on a maintenance charge till neded?  Or will I need to charge them one at a time.

ANSWER: I would hook them up in parallel and then put my charger on the negative of the battery at one end and the positive of the battery at the other end.  This will distribute the charge evenly.  Also I would recommend the Battery Tender Junior for most sub 100 Ah batteries (and battery banks).

On February 17, 2011 at 3:54am
Ruairi wrote:

I’m Trying to determine the state of a battery.: Is this normal or do I have a fault?
It’s an Elecsol 220 AH battery. This is a sealed flooded cell, using “carbon fibre” technology, and is sold as a “Full Traction design”.

I tested this battery, It initially read 12.76V, and I had applied a top-up charge using a 600ma smart charger intended for smaller batteries.
It’s magic eye was not showing “Green”

I connected a paralell series of 3x 15 ohm,  and 3x 22 Ohm, 10W resistors, with a 1 ohm 10W resister in series with the combination, to use as a current indicator. The whole circuit measured 4.0 ohms, and the 1ohm resistor measured 1.0 ohms using my multimeter.

As expected on connection, the voltage dropped very quickly, and the current was below what would be expected for the voltage. this transient effect took about 30 mins to stabilize, when the current rose suddenly.

I believe this effect was due to thermal changes, and a delay in the chemical reactions in the battery, mentioned elsewhare in article on battery perfomance.

Until 17 hours the voltage and current tapered off very slowly, dropping from 12.29V to 12.07V (in circuit, measured across the battery terminals)
in this time the current dropped from 3.29 to 3.229 amps, ,measured as a voltage across the 1 ohm resistor.

over the following 10 hours to 25 hours the voltage and current fell away very quickly, though as I was not in attendance only 2 data points were obtained. at 18 hours the voltage was 11.59V and current was 3.096. at 25 hours, the Voltage was 11.04, and the current was 2.943
when viewed on a graph, the step chance in rate of fall of voltage and current is very visible, looking like a precipice.

after resting for 15 hours, the open circuit voltage reads 12.26 Volts.

Most guides to rested open circuit voltage suggest that with an open circuit voltage of 12.26V, the battery is about 65% cahrged. My own calculations of drain suggest that I have removed 36% of the stated 220AH capacity.
These statement would indicate that the battery is in good condition, and close to stated capicity.

Is the rapid change in discharge curve normal, or does that indicate there could be a fault?

Thank you in advance for your reply.

On February 17, 2011 at 4:09am
Jin wrote:

For god sake, pls don’t answer any question with misleading answers.

-69 Watts x 10 hours = 690 Watts DC (WTF, power x time= power dc?)

-3x 7.5 ah batteries in parallel = to 1x 22.5 ah battery

On February 17, 2011 at 4:12am
Jin wrote:

to Ruairi
a shorter question?

On February 17, 2011 at 4:20am
Jin wrote:

To Gonzalo P
plz write clearer. I am not sure what is really you question is, but you can’t change a 12v using 24v power supply.

On February 17, 2011 at 4:25am
Jin wrote:

To John Cocula
again, plz clearer question. R u trying to test the current of ur battery? if so, DONT do it. It is unwise, dangerous and no need to test a battery’s current.

On February 17, 2011 at 4:32am
Jin wrote:

To Vijay Moongilan

it is a bad idea. DON’T try it. The 7 ah will used up first, so u won’t have 24 volt. It is like connecting a dead battery and a fresh battery in series. It won’t work.

On February 17, 2011 at 4:42am
Jin wrote:

to alexander
sry, I am unclear about ur problem. U tested the battery when it is cold? N it reads 12.6? Temperature is a big factor to battery performence. A dead battery in cold will work after it warm up, so be sure to know that Voltage reading is not accurate in winter time.

On February 17, 2011 at 4:51am
Jin wrote:

To Tajammul
I am sure your battery is fine. Probabaly want somebody to check your car.

On February 17, 2011 at 4:59am
Jin wrote:

To Gonzalo P
u r right. They should be in parallel. Since ur device uses only 200ma, you only need a charger with 200ma. Think about it. It is simple. No battery: a 200ma power supply will power ur 200ma device constantly. No device:  a 200ma power supply will charge your battery. No power supply: ur battery powers ur device.

On February 17, 2011 at 5:04am
Jin wrote:

to cornflake
it is possible. You need a dc-to-dc converter which is more expensive than replacing your 12 v battery.

On February 17, 2011 at 5:13am
Jin wrote:

To Hesham Mohamed Homam Al Hashemy

1, no, more than 10 hrs
2, yes,
12v x 1 a = 12w
6v x 1 a = 6 w
so a 12v charger is faster.

On February 17, 2011 at 5:22am
Jin wrote:

This page is a good reference about lead acid Battery charging, but few points are incorrect, but not fatal mistake.

Any more question. Email me.  I am not only a total expert in batteries, But in electronics 2.

On February 17, 2011 at 5:53am
Jin wrote:


You need to know wt kind of charger you have. A smart charger may need you to choose some options before it works as designed. A simple charger will easily damage your battery if misused. Worst, some cheap charger will damage your battery either way. I use a charger which was designed and built by myself. It is best if u built ur own charger, or you really want to get a more expensive smart charger.

On February 17, 2011 at 11:35pm
George wrote:

Question? I am real stupid with these things. I have it that (re)/charging time is Ah of battery devided by charging amps which means a 100Ah battery recharges with a 7.5A charger in 13 Hours? If I draw 30% from a fully charged battery can I make the assumption that the recharge will take 30/7.5 thus 4 hours?

On February 20, 2011 at 8:10am
Ramya wrote:

I am a student from India. I would like to know the lead content of different types of Lead Acid Batteries.

On February 21, 2011 at 8:45am
AnRuaRi wrote:

Summary for Jin of my previous Question:
I bought 2 2nd hand large capacity batteries. I set out to test them to determine if they are working correctly for a 2 year old battery.
I set up a 50W network of resistors to create a loat to discharge them and graphed the in-circuit terminal voltage and current over a period of 25 hours.

The Terminal voltage initially dropped very quickly from it’s resting state, then took about 30 mins to stabilise. It dropped slowly over the next 16 hours (to about 12V, then fell much more quickly over 8 hours to about 11V.
The rested open circuit voltage was then about 12.2V
The calculated AH removed from the battery and the open circuit voltage after the test both indicated about 40% drain re the stated 220AH capacity of the battery.

is it normal to have this type of shape to the discharge curve:
30 mins. stabilisation time initially.
sudden rapid drop in in-circuit terminal voltage of batter at about 30% discharge (i.e 70% remaining)?

On February 21, 2011 at 8:49am
AnRuaRi wrote:

Follow Up Question: Is this normal?

same set-up as in previous example. 220AH Battery, 4ohm discharge circuit. discharge test over 27 hours.

The second battery presented with significant fluctuations over the first 4 - 6 hours of the test, with in-circuit terminal voltages varying from 12.1V to 12.4V, going up and down over the 4 hour period before stablizing at 12.2V for about 10 - 12 hours.

Is this normal of a symptom of a problem in my battery or circuit?

On February 21, 2011 at 11:24pm
Javed wrote:


I want to know if a 12v, 500mA dynamo can be used to recharge a 6V, 4AH lead acid battery with suitable circuitry???

On February 22, 2011 at 12:38am
Sandip wrote:

What is initial current in battery, I want to connect 2no. 12V 42AH batteries in parallel for better capacity.
How much charging current is required for charging above batteries in parallel connection condition. I have a 10A,12V charging machine.

On February 22, 2011 at 5:14am
Jin wrote:

To AnRuaRi

so you have discharged your battery using a 50W load with 4 Amps current?  (4 Amps X12.3V=50W) Since 4 amps is your discharge rate, if you have a 220ah battery, then 220/4=55 hours. Have you charged your battery before discharged it? Did you discharge your battery for 55 hours? About your testing circuit, have you used an ampere meter to measure the current? Are your resistors rated at 50W and are not hot to touch?

PS.This kind of discharging test is really not necessary and it is unwise because it will damage your battery.

Answer your question;
Your discharge curve is normal. Terminal Voltage will drop and fluctuate once a load is applied to it. Once you remove the load, the terminal will return to its maximum voltage. In your case, it is 12.2V which is less than 50% capacity; so if you have discharged it for about 55/2=27 hours, then your battery is in a good shape. voltage is not an accurate way for measuring the capacity of a battery when it is either charging or discharging.

You probably need to get me more info about your test.


On February 22, 2011 at 5:21am
Jin wrote:

TO Javed

It is easy to charge with a higher voltage to a lower voltage, in your case, a 12V to a 6V. The easiest circuit requires just 1 electronic component which is a 7807 regulator (7 volt regulator). you don’t need any capacitor. It will cost you less than 2 US dollar.

On February 22, 2011 at 5:24am
Jin wrote:

TO Sandip

2X42AH=to a new 84Ah battery. You can basically using any current to charge this battery. The problem is that this is a big battery. Little current will take forever to fully charge it up, so you can safely charge it using 10A.

On February 22, 2011 at 5:27am
Jin wrote:

To George

30% = 0.3

and there is an inefficiency factor you need to consider.

On February 22, 2011 at 10:56pm
javed wrote:

thanx jin,

I have one more question…..

i want to know if i can simultaneously draw power from a 6v 4Ah lead acid battery while   it is charging???

On February 23, 2011 at 5:24am
Jin wrote:

To javed,

It depends. Since you have a 500mA charging current, you can’t continually use more than 500ma for 13 hours. (4 AH/ 0.3A= 13Hr) The battery will be drained, but Yes, you can simultaneously draw power from a 6v 4Ah lead acid battery while it is charging, if your device consumes less than 24wh of power which is the capacity of your battery. (4ah X 6v=24Wh)

So how much is 24wh of energy? if you battery is used to power a high power LED of 3.6V at 700ma (3.6V X 0.7A=2.52W) , 24wh of energy is good for about 9.5 hours of lighting. (24wh /2.52w = 9.5 hr) You will for sure get less than 9 hours because of the inefficiency factor.

On February 23, 2011 at 5:31am
Jin wrote:

I probably make it too hard to understand. To simplify what I have said above, the answer to your question is yes, but if you continually use more power than you have provided from the charger, then the battery will eventually drained.

On February 24, 2011 at 3:34am
Robert wrote:

Please visit our website to learn more about lead acid battery charger. We make 8 steps charging, reconditioning, and testing of battery in one charge cycle. Simple and safe to use.

On February 24, 2011 at 8:37pm
syed hyder wrote:

my question , i have 150AH 12V battery, with an automaticUPS system , it is only 12 months old , but it doesnt seem to give enough power
what to check

On February 25, 2011 at 2:43am
Aamir wrote:

Dear Sir
I have a digital Mulitmeter and want to test 12 volt/ 24 ah batery

Please guide me how i can test a battery through digital multimeter

where should i apply range and what is accuracy of test

On February 25, 2011 at 3:41pm
Cadex Electronics Inc. wrote:

This article has been updated as of February 25, 2011.

On February 25, 2011 at 5:25pm
Jin wrote:

there are still a lot of minor mistakes in this article such as “During the constant-current charge, the battery charges to 70 percent in 5–8 hours”, if you have a 200ah battery, 200ah/8h*0.7= 17.5A, without considering the inefficiency , you have to use at least a 17.5 amps charger, and if you don’t have a 17.5 amps charger, then there is no way the battery can be charged to 70% in 8 hours, so the first graph should be amps against capacity instead of time. and the charging voltage can be used from 2.3-2.5v per cell instead of 2.3-2.45V.

On February 26, 2011 at 11:24pm
Raja wrote:

dear sir,
  Recently i joined in Battery industries. i am interested to know about charging. How there are calculating the Capacity (Ah) in Theoretical Manner and how they are applying the Practical Ah to the battery.
  For Example,
            I am charging 120 AH Battery with 7 A so i should charge up to 17.14 h.
then how much they are applying the excess charge to that battery. Particularly How much they are applying the Excess percentage to the Practical Applications.
            When charging they are maintain the rest to control the temperature of battery while charging. What should be the Max Temperature allowed to the Lead acid Battery.
            Can you give your ideas to me to know about charging. i am waiting for your kind reply from you. i hope you will clear my doubts.

Thanks and Regards


On February 26, 2011 at 11:32pm
Raja wrote:

Dear sir,
          when we charge the battery the Specific Gravity of Electrolyte increase. Is it Possible to find out the Value of S.G with Voltage before Charging what will be the Values if them corresponding to our Charging Current with duration.

Can you explain with one example.

Thanks & Regards


On March 2, 2011 at 9:33am
Cadex Electronics Inc. wrote:

@Jin: The 70% SoC mention does not relate to charge currents and applies to small and large batteries.

On March 4, 2011 at 3:07pm
Cadex Electronics Inc. wrote:

We have updated this article with new information.

On March 4, 2011 at 9:38pm
Noah wrote:

Ya my name is Noah and I took acid from a fourwheeler battery and put it into a smaller motorcycle battery and it bubbles while it is on ten amp what shod I do

On March 7, 2011 at 4:51am
Morteza Nasooti wrote:

please add information about the lead acid batteries’ operating temprature range and what we need to do when the battery room temprature becomes below -20 deg cent. in the winter

On March 12, 2011 at 5:09am
Francesco wrote:

HI, I have a question. I charged a new battery after adding the acid at 12V with 1.5ah. Did I screw the battery or can I recover it with a “smart” charger that follows your above figure?


On March 16, 2011 at 4:51am
Kannan T wrote:

Dear Sir
            if you have data for SONY US 18650 battery (1.4Ah,4.2V) please send to me that’s very useful to my work

Kannan T

On March 17, 2011 at 9:24am
Kevin Fletcher wrote:

I have recently received a sample rechargeable battery with the vent cap blown off one of the cells. and the back of the cell swollen.
This is an 18v battery consisting of 15 cells 1.2v 1700ah Ni-Cd.
Is this a weak cell in the chain, having a chemical imbalance during charging / discharge
and why is the vent cap… not venting. ??.
Is it is a sudden build up of reactive gas. ?

On March 18, 2011 at 5:27am

Dear sir , i am planning to take a Amco battery dealership so my kind request to you that pls provide me the information about how to charge a conventional battery ,mf battery, ups and inverters waiting for your reply
thanking you

On March 18, 2011 at 8:48am
Mike wolf wrote:

I have a new but completely dead Optima battery. My two chargers won’t charge it because they are “smart” [dumb] chargers. To fool the chargers into starting I need to add a second battery. Do I hook the two in series or in parrallel?

On March 22, 2011 at 1:09pm
Bill Yacey wrote:

I have an SCR controlled charger that I built. It has separate controls to set the on threshold and the off threshold. For a wet 12 lead acid cell, should i set the on threshold at around 12.8V, and the off threshold at around 14.5? with the charging window set this small, it tends to pulse a fully charged battery occasionally. Is this an acceptable condition?

On March 23, 2011 at 1:41pm
Blair wrote:

Dear sir, have you ever analyzed the amount of lead contamination in battery acid or are you aware of any data dealing with sampling/characterization of lead contamination in battery acid?

On March 23, 2011 at 1:43pm
blair wrote:

I forgot to add in my previous note “Notify me of follow up comments” dealing with lead contamination in battery acid.


On March 27, 2011 at 12:23pm
jim hamlett wrote:

why does a 12 volt lead caid battery hold 12 volts and very low on amps?

On April 2, 2011 at 1:44am
Soto Ndiaye wrote:

I need some documentation about Trickle charging Lead-acid batteries algorithms and new Lead-acid Batteries charging algorithms witch can be applied for any type of Lead-Acid Batteries. Any document or information could be helpful for me.
Please could you send me (asap) some documents/information about this subject?

On April 6, 2011 at 6:19pm
max wrote:


I have a 12v 10ah sla battery. It shows 13v with a multimeter. When a 50w load is applied the voltage drops to 10v. Is this battery dead??

Thanks in advance


On April 10, 2011 at 6:43am
John Fetter wrote:

Pulse desulfators came out at the same time battery manufacturers switched from hybrid lead-antimony positive and lead-calcium negative grids to lead-calcium-tin grid alloy. Tin is added to stop surface passivation of the positive grids, which results in batteries going “ooen circuit”. Tin is sensitive to concentration. Below 1.5%, the benefits of tin reverse.
The problem that is being solved by so-called pulse desulfators is not as much sulfation as “open circuit”. The surface passivation consists of an oxide of lead and is very thin. Strong pulsing punches through, restoring battery ampere-hours dramatically. If it was sulfation, the cure would not be as dramatic.

On April 20, 2011 at 4:44am
asef wrote:

please send me charging and decharging curve of seald lead acid 2 V

On April 30, 2011 at 11:49pm
mike wrote:

I have a question…..or two….
If I had a 12V deep cycle battery and i depleted it to 30% or 50%, how long would it take to charge it to 90%-100% power using a typical 13.5v alternator?

On April 30, 2011 at 11:52pm
mike wrote:

and the other question is the same except with a reg, car starting battery.

On May 1, 2011 at 1:58am
asef wrote:

thanx alot…

On May 1, 2011 at 7:44pm
Art Jackson wrote:

I have some old 2vold lead calcium cells that I am trying to maintain/recover. They we used when I obtained them at least 10 years ago!

The cells are C&D Type DCU 13 . lead calcium cells rated at 8HR CAP 150 AH
Date of manufacture was October 1984!

For many years these have been used only occasionally to power my ham radio station and were recharged by “guess and by God” using an older so called “automatic” automotive battery charger then maintained by an unregulated 1Amp solar panel. The charger went on again whenever battery voltage dropped below 12.6V (which was seldom). I later built and connected a variable voltage power supply which will supply 1 amp of pure DC at voltages continuously adjustable from 7.0V to 29.5V

For the last 5 years or so this supply has been connected constantly set at 13.2V except when we leave for the winter and I drop the voltage to 12.8 as I don’t want to risk losing water.

Also during at least the last 5 years the battery charger used to recharge after use has been a three stage “smart charger” which will supply up to 40 amps. I disconnect it after it reaches the float stage, leaving the 1 Amp supply in circuit.


This year we were away for 10 months and on my return I found that

1)  I had inadvertently readjusted the float voltage to 12.75 volts

2) There had been multiple power failures during the winter and the house sitter may (or may not ) have used a 12V florescent lamp in the kitchen which is connected to this battery.

3) Fluid levels were adequate on my return. Battery charger was attached, limited to 30Amps and ran it’s cycle.

4) After charging SG is as follows:  1.225, 1.225, 1.225, 1.200, 1.225, 1.225

I have run a short (30 minute) pulse desufation   charge ( a function of the automotive charger)

THEN I decided I should look for more information from more informed people and asked Mr Google for help and here I am!

Am I too late? Any thoughts or suggestions?



On May 4, 2011 at 11:51am
Darryl wrote:

I have four new 12 volt amg motorhome batteries connected in parallel. what battery tender (charger) spec should I use.

On May 4, 2011 at 11:55am
Darryl wrote:

addition to above message- the motorhome is in storage for 3 months

On May 4, 2011 at 12:10pm
Darryl wrote:

correction to above two postings- the batteries are agm (glass matt)

On May 6, 2011 at 9:19am
Art Jackson wrote:


The battery manufacturer should have recommended charging parameters. AGMs charge differently than flooded cells as you probably know, but each manufacturer seems to have slightly different parameters.

What is the charger in the rig? Converter? Inverter/charger? What make/model.

My Xantrex Prosine 2 inverter/charger has settings for generic AGMs and I can also setup a specific charging algorithm.  Wish I had AGMs!

On May 8, 2011 at 5:42pm
Al wrote:

I am interested in building a 260ah bank using two 6vdc deep cycle batteries in series. My question is after reading several articals suggesting charging rate of 10% AH (so 260AH deep cycle should be charged at 26A) I already own a smart charger with the maximum settiing of 12A. Will this be ok to use? will it damage the batteries? Im thinking it will just take a lot longer to reach full charge. Should I invest in a much more powerful charger or use what I have and just wait for a longer charge cycle to finish?

On May 8, 2011 at 7:53pm
Art Jackson wrote:

Most deep cycle batteries, especially the 6 volt “Golf Cart” batteries can take much higher charging current than than 10% of the AH Capacity. C20 is common as is C30 and even C40 in some instances, though as a rule that’s pretty hard on the batteries.

Charging at a lower rate will not hurt the batteries, it will just take a much longer time to reach full charge.  You have to be aware that charging rate and current is not linear: A “Dead” battery, at 10.5 volts will accept a lot more current than one at 50% State Of Charge (roughly 12.2 volts) and one at 80% at 12.5V. Charging current will taper off as full charge approaches.

If you can afford the time, probably 24 hours or so, then go with what you have.

Remember too that the 260 AH is from fuul to dead. Dead is not good for battery life (that sounds a bit strange doesn’t it?!) Best not to take them below 50%, ie 12.2 volts (no load, resting measurement) then recharge. That really means that a bank of 260AH batteries is in effect a 130AH supply. When I stopped trying to take 320 AH out of my 4 group 24’s they didn’t have to be replaced every 1 o r2 years!

Another good site for battery charging info is www.rv.net. Go to forums, tech issues and be prepared to spend a lot of time reading!

On May 12, 2011 at 6:27pm
al wrote:

I currently own a motomaster eliminator intelligent battery charger to charge 12v lead acid batterys. It charges AGM, DEEP CYCLE or REGULAR batterys at 2/8/12A. If the battery is sulficated it will try and fix it. after the charge cycle compleates it float charges them and monitors them. I am looking to purchace a more powerful charger. Maybe-40 to 60A. I Does anybody know of a decent charger that does all of the above and maybe more!! I would like to reserch products before buying so brand names /manufactures of such device would be very helpful. Thankyou

On May 12, 2011 at 7:27pm
Art Jackson wrote:

I have the motomaster eliminator 40A version and have been fairly happy with it. It did recover 2 group 24 batteries that each had one low cell. If you keep your eyes open Canadian Tire often have them on sale at 99 in stead of 149.

On May 27, 2011 at 10:32am
Smarties wrote:

Is there any implication apart from an extended charge time of charging a 12V lead acid with a charger who’s constant current rate is well below the 10% of AH rating.

Example - 10AH and 300mA charger.


On May 27, 2011 at 3:41pm
John Fetter wrote:

Lead-acid responds very well to slow charging. If possible, aim for a 3 to 4 day charge and battery life might well double. The faster L-A is charged, the greater the risk of positive grid corrosion. The only reason batteries are charged in hours rather than days is because most people simply cannot wait.

On May 31, 2011 at 3:41am
dapo wrote:

I have a question: I have a battery bank of 4 pieces of 150AH lead acid batteries used for a 3.5kva inverter system. I am yet to achieve a full charge as I charge for about 5hrs daily at 170vwith 16A charging. What is the max time to get full charging.
Also if I double the battery to 8 batteries, will the charging time double?

On June 6, 2011 at 3:06am
dylan wrote:

I need some help with the estimation of state of charge of a 48V lead acid battery.

I need to measure the state of charge of the battery in a continuous manner like a battery monitor. What method should I employ? I guess the voltage method wouldn’t work, because I need to measure the battery SOC when it is discharging so that I can charge it when it is below a certain SOC and stop charging it when it is above a certain SOC.
Please help me.
Thank you.

On June 6, 2011 at 3:08am
dylan wrote:

I have no other info on the battery. I can measure the battery voltage and also have a current sensor.

On June 6, 2011 at 10:30am
Art Jackson wrote:


A couple of questions: What voltage are your batteries and are they in series, parallel or series/parallel. ie what is the output voltage: 6, 12, 24, 48 etc.

4 150AH batteries in Parallel will have a total capacity of 600AH, at the same voltage.
4 150AH batteries in Parallel will have a total capacity of 150AH but at 4 times the voltage.

It also depends on what type of battery: flooded wet cel;, gel cell, AGM—all charge slightly differently.

I charge at at the 20C rate, that is, 20% of the total AH capacity of the batteries. Some manufacturers say more, some less. It is usually safe to charge at 30C and some AGMs can accept an even higher charge.

SO if you batteries are all in parallel, ie 600AH total, at 20% the initial charge current could be as high as 160 amps.

At 150AH (all batteries in series) 20% is 30 amps.

It would appear that you are charging at somewhere between 2 and 10 percent of Amp/Hour capacity. 5 hours won’t be nearly enough.

To borrow a phrase from a friend, think of charging time as a frog jumping along a long. Each jump takes as much time as the previous but for only half the distance. In theory he will never get to the end.

From 50% charged (12.2V in a 12 volt battery) to 80% (12.4) will go relatively quickly but the last 20% will take much longer as charge current becomes limited buy the batteries.

There is nothing wrong with charging slowly (Unless of course you are in a hurry!)

There is lots to learn about battery charging. Another good source of information can be found at www.rv.net forums in the tech issue forum.


How are you measuring SOC? I am assuming SG.


On June 9, 2011 at 8:25am
Ronald Beal wrote:

Thanks sooooooooooooo   much.  Your help is right on time…

On June 25, 2011 at 4:01pm
Anthony Gomez-C wrote:

5 months ago I bought a brand new Lead - Acid Battery, 12v., 73Ah. 1.250g/ cubic cm., 11 Plates (Placas) 20ºC for my Land Rover, which was installed but disconnected.  2 months later I connected the Battery, pressed the starter button and away we went I only used the car twice for two hours at a time, all was fine,
disconnected the Battery and went away for 6 weeks, came back connected the battery and ............. nothing happened, apparently this New Battery is now completely discharged, although the water level is OK. and was left at an average temperature of 12ºC.  I Tried to charge it with my 15 amp. charger, but no luck, the voltage is OK, but the discharge is a mere 5 miliamps which is nothing. Can this battery ever be charged again.  Do I need to empty the liquid (Acid) clean the plates with something liquid then fill the cells up with new Acid, or is there some other method to save this New Battery? Will appreciate any advice. Thank you. Anthony

On June 27, 2011 at 4:57pm
Art Jackson wrote:

You have probably lost the battery due to it being stored in a discharged state.

Do not change the electrolyte. If the specific gravity is low it is because of the sulfate being deposited on the plates instead of being in solution. Changing the electrolyte, or adding more acid won’t help because of the sulfate already built up on the plates.  There is no way to clean the plates except possibly by using a battery desulfater. Some battery chargers have a desulfate mode, sometimes called a reconditioning mode.

There is a very small chance that you can recover the battery but is it unlikely. Sometime a low current charger (just an amp or 2)  left on for days or even weeks can help.

If you didn’t charge the battery before installing it and leaving it disconnected it may well not not been fully charged. Frequently so called charged and ready to go new batteries are not at full charge.  Leaving them for another two months would have allowed them to discharge further and continue to d\sulfate. A couple of hours charging from the vehicle alternator may not have been enough to fully recharge, and then there was another 6 week of sulfating.

A couple of question: What is the battery voltage now? Do you know the specefic gravity? Both these should be checked and recorded.

Check the voltage as it is now, connect your charger and let it run until it shows charged or at least 6 hours which ever comes first.

Next check voltage and specific gravity again. Note that the voltage will be artificially high due to surface charge. Let the battery sit for 24 hours and check the voltage again.

A new fully charged battery should have a SG of 1.265 or better. 1.200 is poor (1.000 is pure water!)

A fully charged “12 volt” battery will be at about 12.6V The charger may well take it up to 14.4 or so while charging.

About 12.2 volts is 50% and 11.8 is approaching dead. (these voltages at no load, the battery at rest)

Anything under 11.0 may indicate a dead cell. This also could be your problem.

One other question, how did you measure the discharge current? Was the starter engaged at the time, lighs on? Please let me know here. I will try to remember to check back here over the next few days for your replies.

One last thought. Did the battery come with a warranty or guarantee? Many companies offer full one year replacement warranty.

Let us know what you find.

On June 28, 2011 at 4:01pm
Anthony Gomez-C wrote:

Hello Art Jackson.

You have been extremely helpful.

This is what I can tell you so far:

All six compartments (Water top-up holes) are still at their correct level.

I have a specific gravity measurer, the one with the 5 colored balls inside a glass tube.
0 balls rising = discharged, 1 ball rising = 25% charged, 2 balls = 50% charged, 3 balls = 75% charged, 4 balls = 100% charged and 5 balls = very charged.
Amazingly all six battery compartments read 75% charged!?

I have a charger on at the moment, at full charge, but it is only charging at 0.75 milliamps.
The voltage from the battery (with charger disconnected) is 11.5 volts, but when connecting a small dash board bulb, it lights up, the bulb being 12v and draws 150 miliamps, any higher rating bulb will not light up.

I measured the discharge currents with the battery completely disconnected as with all my readings, and put my ammeter across the battery terminals.

I think the battery came with a warranty or guarantee, but as I have never come across the existing trouble over a 50 year driving experience, did not keep the Receipt! There is always a first time, even if it took 50 years!

From what I deduct, the battery is 75% charged, but can not discharge large amounts of current?


On July 9, 2011 at 2:34pm
Kenneth Cary wrote:

?? Do I have to disconnect one battery from to other or can I leave them hooked up together to charge. They are 12 volt batterys but I have them hooked 24 volts for my trolling motor

On July 10, 2011 at 4:07pm
Anthony Gomez -C wrote:

Hello Art Jackson.
My case seems to be rather strange!
Before charging the battery the voltage is 11.
After charging the battery the voltage is 12.
The SG before and after charging is still 75% charged? and this is how the battery was found before doing anything to it ?!!
First the starter would not operate, tried the head lights, no go either, all it can light up is a dash board small 12v bulb, bit with an intermittent glow,it glows then goes off, then it glows, then goes off at 2 second intervals!  The discharge between glow and no glow varies between 40 miliamps to 90 miliamps. If I short circuit the battery via my ammeter the discharge is the same.  It seems that the battery can not discharge its 3/4 capacity (SG 75% charged)! Perhaps it needs to be on a continuous discharge, although as mentioned, the discharge would be only between 40 and 90 miliamps.
Not sure whether my battery came with a warranty or guarantee, can not find the receipt.

On July 17, 2011 at 3:15pm
Anthony Gomez_c wrote:

Hello Art Jackson.
My case seems to be rather strange!
Before charging the battery the voltage is 11.
After charging the battery the voltage is 12.
The SG before and after charging is still 75% charged? and this is how the battery was found before doing anything to it ?!!
First the starter would not operate, tried the head lights, no go either, all it can light up is a dash board small 12v bulb, bit with an intermittent glow,it glows then goes off, then it glows, then goes off at 2 second intervals!  The discharge between glow and no glow varies between 40 miliamps to 90 miliamps. If I short circuit the battery via my ammeter the discharge is the same.  It seems that the battery can not discharge its 3/4 capacity (SG 75% charged)! Perhaps it needs to be on a continuous discharge, although as mentioned, the discharge would be only between 40 and 90 miliamps.
Not sure whether my battery came with a warranty or guarantee, can not find the receipt.
Thank you,
P.S. This is my third attempt to publish this information!

On July 24, 2011 at 10:30am
mike wrote:

so lets say i drained my battery supply to 70% and i wanted to recharge it to 90-100%, what would the estimated time be to recharge it?
the battery has 115 amp hours.

On July 29, 2011 at 12:30pm
Daniel T. Le wrote:

I have two 12v 4.5Ah (20hr rate) connected in series for a toy and I also have an addapter with 2 outputs: 32v-375mA or 16v-500mA want to use as charger for the above batteries, can ?? Which voltage should I use and how long should I recharge for or what should I do with what I have for what I need.

On August 11, 2011 at 9:04am
Kanagasabapathy wrote:

Is it possible to recharge a 100 Ah - 12 volt Lead acid battery using a self designed charger with 1A -14 volt? Kindly en light this.

On August 11, 2011 at 7:22pm
M Kanagasabapathy wrote:

Is it possible to recharge a lead acid battery 12V - 80 Ah - C20 by using a charger of specification 14 V -1A. Kindly explain.

On August 11, 2011 at 7:25pm
Kanagasabapathy wrote:

Is it possible to recharge a lead acid battery 12V - 80 Ah - C20 by using a charger of specification 14 V -1A? Kindly explain.

On August 15, 2011 at 3:57am
Jacko wrote:

New question , battery charging with solarpower..
I’ve got 2 Hawker energy SBS60 12 V 50,8Ah batteries.
Float voltage of 2,27v.
So each battery give me 12v x50,8ah x30% = 183Watt x2 = 366w with 2 batteries.
so when i put these in a camper and want to charge them with solarpower…
How do i have to calculate the charge value coming from the solarcells for those 2 batteries ? when in the same time a charge is taken from the batteries by Frigo, laptop,waterpump,led lights etc..about 300watt a day ..

What i want to know = what has to be the value of the solarcells to keep this system good working ...50 watts…70 watts…? or more

Batteries connected parallel i guess or seperated and working with a divider who charge each battery when other is full and then change again ? ..what would be the best solution..

any idee about a good solution is welcome..

greetings jacko (Belgium)

On September 16, 2011 at 9:48pm
jin wrote:

Totally right.

On September 19, 2011 at 10:33pm
yi yew wrote:


How to calculate the minimum amp to charge two 6V sealed lead acid battery connected in parallel?

On September 22, 2011 at 8:42pm
Victor Barbarick wrote:

I have 4 Trojan 6 volt T-145 (145 minutes @ 75amps)  golf cart batteries connected in series/parallel in my RV. After storing the RV for several months the batteries hold a charge but drop to about 12vdc.  My question is that when I charge them with the RV inverter/charger they will continue charging in the bulk range up to 14.5 for a period time with the battery temperature at 100 degrees Fahrenheit and the batteries with the batteries gassing to the point that I need to add water to cover the plates.  Is this normal??

On October 3, 2011 at 2:15am
Moti Mazor wrote:

1.  If you connect 2 or 4 lead acid twelve volt batteries in parallel only for charging .
Please let me know if tis is ok and acepted?
2.  Can I charg batery with power supplay ( 14.5 V ) with out any serial resistance for limiting the curent ,  and not with special charger for batterys?

On October 14, 2011 at 5:37am
Tommy lee Singh wrote:

hi, i charge a car battery for a friend every day,(the battery is used for lights and cooking and other daily activities etc), it charges on low. i tried to charge it on high but it begins to bubble. i would like to know how much is this going to cost me per month if a have the prepaid system and charge this battery everyday on low. the charge per a kwh is 65.06c in south africa. will appreciate a response.

On October 14, 2011 at 5:44am
Tommy Lee Singh wrote:

hi i charge a car battery for a friend everyday,(the battery is sed for lights, cooking and other daily activities) i charge ut on low. i tried to charge on high but it begins to bubble. i would likje to know how much it is going to cost me if i charge it everyay on low for a month. the charge per a kwh is 65.05c in south africa, please help.

On October 17, 2011 at 7:00am
mohammed habiibullah wrote:

i have a brand new set of 12volts lead acid battery, i should install the battery and start using it what is the quantity of acid and distilled water in ratio to be added and put for charge , and should i added acid or distalled water , kind of charge low ampere or trikle charge

On October 17, 2011 at 10:15am
Niketan wrote:

How many cells are there in APC RBC 17 battery? It is a 12v, 7AH battery.

On October 21, 2011 at 6:22am
tommy lee wrote:

i asked a question about a week ago and still no reply. disappoionting!

On October 24, 2011 at 12:29am
Marwa wrote:

I read many battery charger specs that are used with hybrid wind-solar LED street light systems, some of them mentioned the following:

1-The charger is protected from over voltage when there is no battery or when the voltage at the input exceeds certain limit.

2- When we may need the open circuit protection when there is no battery?

Kindly elaborate on the above two points

Thanks & Regards

On November 7, 2011 at 9:57am
Rajaganesan wrote:

dear sir,
        In Lead acid battery at formation, they are calculating the 3 wt % SO4 from positive and 3.45 wt % from the negative paste, or 72 g. This is equivalent to 73.5 g of H2SO4.

        The concentration of H2SO4 in a 3 wt % solution is 31 g/l. In which PbSO4 = 112.53 kg with the wet paste weight = 1182.8 kg.

          I want to know how they are calculating 72 g and 31 g/l.  I am waiting your favorable reply

Thanks and Regards


On November 11, 2011 at 10:17pm
Don Rose wrote:


Is it true that lead acid batteries should be cycled from time to time by at least a 5% discharge? Or is this an “old wives tale”?

On November 22, 2011 at 9:51pm
pushpa T S wrote:


i want to measure the battery capacity ??????  i need to charge the battery accordingly by measuring the battery capacity

On December 15, 2011 at 4:16am
eliseo viray wrote:

sir, i need to know what charger will i use to charge 15 to 20 units of 12v 100ah batteries in one charging

On December 18, 2011 at 11:17am
P.K.Jain wrote:

I have discovered that I have 100 Nos 12V-26AH SMF LA UNUSED Batteries lying on shelf unattended for 4 years. The batteries show OCV of 2-3 VDC. How in this world can I revive them. Slow charging or Pulse Charging? Kindly refer resources where I can study the methods of reviving dead batteries.

On December 19, 2011 at 9:57am
Ken wrote:

Sorry I come into this late but I would like some thoughts on some backup system I am setting up.
My Charger is limited to 10Amp
200AH vrla gel 12v batteries
48vdc system with 4 strings (4x4 = 16 batteries )

What is the estimated time my charger will need to bulk charge the batteries ?

On December 21, 2011 at 7:42pm
mattymays wrote:

hi batteryuniversity.com-ers all the best   to every one -  matt

On December 29, 2011 at 9:32pm
Bob K. wrote:

Did your DCU 13 cells restore or di you happen to open them to see what was inside?

I have started playing with some Rolls S-460 (350AHr) batteries and I need to select a scheme to minimize water loss yet prevent acid separation and sulfate build up.

Any ideas out there?

Bob K.

On December 30, 2011 at 2:40am
John A Bean wrote:

I have 3, 12v 14amp (almost new) AGM deep cycle batteries that were use on a 36v scooter. I plan to add one more for a 48v scooter. When I charged them individually to top them off before I chained them, one battery gets to 13.1 volts but quickly drops to under 12 volts in a day or so when taken off charge. The other two get to 13.2v and stay at about 12.8 volts for several days. My question is; does this drop in the third battery indicate a bad cel and should I replace it before I install four batteries for this 48 volt system? How would it affect the system by using it?

On December 30, 2011 at 3:30pm
Jay Atkinson wrote:

You all are a great resource, thanks in advance for any help you might be able to provide.  We got my 5 year old a little ride on electric car with a weight capacity of 88 lbs this week.  It has a 12V 7ah battery.  The manufacturer recommended a 15 hour initial charge, which we did.  It worked for a couple hours after that charge, which seems about right.
Subsequently, we charged it for 8 hours, also based on recommendations.  After the charge, it sat overnight, and then only ran for about 20 minutes when used the next morning.  I don’t know if the battery isn’t charging, or it isn’t holding a charge.  The charger does not have an indicator light so that’s no help.
Any assistance or advice would be greatly appreciated. Thanks!

On January 4, 2012 at 9:44pm
Anand wrote:

Very useful information for me. I am using a 35Ah flooded lead acid battery(labelled maintainenc3 free) to receive charge from my 100W solar panels, using a charge controller. The battery appears to charge quite quickly using 3-6A for a period of 4 hours. The battery reaches 14V mark, where in the charge controller seems to send reduced pulses of current. I thought the battery was fully charged and the charge controller was wrongly sending current. Needless to say, the battery displayed very less capacity while being used with an inverter. Now I knwo it is due to the absense of the stage 2 of lead acid battery charging this is happening. So, thanks for the info.

On January 5, 2012 at 11:21am
David wrote:

I have an equipment which uses two batteries HITACHI HP38-12 (12V, 38AH) in series. It functions for 3 hours. Can I replace them with two CSB 12V-34AH compromising only the operation time? Can it overheat?

On January 5, 2012 at 7:18pm
Tommy Mak wrote:

If a 12V battery can support 160W for 20 minutes and I connect 2 of these batteries in series, can the assembly support 320W for 20 minutes? If so, is it because the discharge current has been halved?

On January 6, 2012 at 1:54am
Badr wrote:

I have a kende 20A charger and 150ah battery.
The charger is single phase. when I charge the battery the voltage goes up to 19.5v. once I disconnect the charger the voltage drops to somewhere in 13v.
what this high voltage indicates. do I need to replace the charge.
by the way. when the voltage is 19.5 the current charging current is 7amps.


On January 7, 2012 at 11:35am
Ralph Wanka North Bay ON wrote:

Dear Sir,

My 2004 Cayenne has killed 3 Motormaster MOT-49 batterys.
all with in 20 -30 days.
SUV will not start… remove battery bring to CT ...they put battery on Charger / Tester
Tester Goes thru cycle and TEST come out ” Battery HOT “
? Cell bad or what? 
They give me a NEW BATTERY. .. this is 3rd time !!!
? Can my vehicle cause this malfunction to a battery?

On January 12, 2012 at 10:07pm
Mike wrote:

Hi, great site. I was hoping someone could help answer the following question.

I have a 12v 80amh leisure battery that I will be using on a small boat to power a few small items like a cd player and a small dvd player. The battery will also be used to start an outboard engine.
When running, the outboard will charge the battery, but only when it is running.

I am looking to fit a solar charger to the battery to keep it topped up when the engine is not running

Can I do this? Will the battery be OK when the engine is running as there will be the power from the solar charger and the engine going into the battery?

Any help will be great,


On January 26, 2012 at 10:30pm
Elango wrote:

    We are planning to install a low voltage (approximately 0 to 5-10v) battery tester/cycler with a minimum of 8 channels to test and determine the charge/discharge characteristics on Li-ion, Li-polymer, Ni-cad, Ni-MH, Lead-acid, and ultra-capacitors. Specifically, we wish to test the maximum safe charge and discharge rates of button cell type samples of the above batteries.
We need to be able to remotely control and receive data from your device through our own proprietary software. The user should be able to program and control each channel independently to determine the charge & discharge curves and other characteristics on the above mentioned batteries. Temperature monitoring on each channel should also be included.

so need to how fast a battery charges & discharges and how to calculate the charging,discharging rates

On January 27, 2012 at 8:03am
Bob Kondner wrote:

  I do this for some of my products using a USB based data acqu unit like the LabJack or USB-1208LS units for about $100 to $200. I write coe in Delphi though you can write this code in anything you wish. Add a couple of relays for switching loads and sources and you have a pretty complete system. You want a DC clamp on ammeter that reads down to maybe 10ma (depanding on your battery size). If i can help ia am: bob at kondner dot com sent me an email.

If you really have a VERY GOOD idea of all your test perameters then maybe you can buy something. But a few relays, wires and 500 lines of code is no big deal for me and I end up with a very flexiable tool.

The key is your ability to write code effectivly, you really need to know how to use an existing code tool or you can spend a hunk of time learning.

Bob K.

On January 28, 2012 at 11:56pm
Devaraj wrote:

dear sir,
we r doing project in hybrid bike using RT 12220 12v,22ah battery in that, can we check battery charge level using multimeter…

On January 30, 2012 at 11:34am
miraj wrote:

hi, it’s great and useful information. i was also planning to charge my motorcycle battery but i m confused with this words written on my 12v motorcycle battery ” recharge at 0.3A 5~10 hours” what does it mean and while charging what amount of volt and amp should be given to charge it.

On January 31, 2012 at 10:55am
John E wrote:

Hello,we need some Battery equipment to buy,i will like to know if you can supply us with any of this.example below:

Sealed Lead Acid Battery 12v,80 to 200ah…for solar backup

Sealed lead Batteries 100 to 250Ahms, 12 to 24vots

Please reply back soon,to let us know if you have any of it in stock,if yes,please advise unit cost for each.

And will like to know if you accept credit card payment.



John Erick

On February 6, 2012 at 5:07am
Rajnikant wrote:

Hello,we need some Battery equipment to buy,i will like to know if you can supply us with any of this.example below:

Sealed Lead Acid Battery 2v,1500 to 2000ah…for tetecom backup

Sealed lead Batteries 1000 to 2500Ah, 2 to 12vots

Please reply back soon,to

Rajnikant Jaipuriya

On February 6, 2012 at 9:35am
Guillaume wrote:

If you are looking to buy batteries, I am pretty sure you are not at the right place.

a) Cadex does not sell batteries, according to their web site.
b) It is not the place to buy any Cadex’s product.

Go on their web site to see what product they offer.

On February 18, 2012 at 11:28am
abhi prasad wrote:

can i charge my 12 v(7 amps) rechargeable battery using a battery eliminator (1-2 amps) but kept at a higher voltage???

On February 23, 2012 at 6:53am
Allexsiss wrote:

i need some help , please!
i have 4 Maintenance-free Lead acid batteries (6 V 4.0 AH/20 HR ) .
each two are connected in series to form a unit that gives an output of 12 volts.
then the 2 units are connected in parallel ...
i’m charging them with a 12-0-12 V / 3 amp inverter ((an AC transformer))
is it ok to use a 16-0-16 V / 5 amp to charge them instead? because the one i’m using is barely charging them and it’s getting very hot after a short time ...
and yes , i’m using them to keep my router running during power failure smile

On February 25, 2012 at 12:00pm
CYRIL wrote:

  I have two (100Ah 12V lead acid flooded) batteries which is in 24V connection using for inverter use. Daily power failure is half hour. Daily recharging time is 2 hours. Room tempetatrure 25degreeC. My desired charging time is 16 hours. I have a digital charger which I can set ampere & voltage. Which also enabled by over charge protection. And I wish to get the MAX BATTERY LIFE. So, How much is the CHARGING AMPERE & VOLTAGE ? The charger is a single stage charger.

On March 3, 2012 at 1:54pm
Engr Omawole E.Itshoritshelaju Alexander wrote:

I found this page interesting because i having problems with charging batteries to full capacity.

On March 8, 2012 at 3:38am
Chris Pollard wrote:

Hello.I have a burglar alarm and the control panel has two 6V rechargeable batteries in it that I replaced recently.The original adapter that was supplied with the alarm that plugs in to the 240v wall socket is a 16 VDC 600 Ma but it is is broken.I have replaced it with a 13.5VDC 1000 Ma and I am using it at the moment but I am not sure if it will be safe, now or in the long term…..Could you advise please….....kindest regards…Chris Pollard

On March 11, 2012 at 11:01am
humayun wrote:

dear all…im from a country where electricity is becoming rare day by day…frequent period of power failures of long durations…in such situation can some body guide me how to get my ups charged as quickly as possible…my system specs are as follows:
one 12 volt,  2kva,  pure sinewave generator/charger, 400 ah gel type sealed battery…can use an other charger in parallel with the one i have to increase the charge rate.. while keeping same voltage…????any answer pse….

On March 15, 2012 at 11:31pm
seyi +2348130567222 wrote:

to allexis: the maximum voltage u cud use to charge a 12v lead battery is 14.5 -14.7v,moreover the current passed on the batteries matters a lot.using a 16v charger cud caused the internal resistance of the battery to rise.

On March 18, 2012 at 10:31am
vikram wrote:

I am planning to install inverter and battery in my village, Here is my requirement :

- 4 CFL + 2 Fan

In my village electricity is for around 4-8 hours daily. I tried to find most suitable battery and inverter for this, but some how could not find right configuration. It would be really helpful if you guys can give some advice on this.

Thanks a lot for your help.

On March 19, 2012 at 8:56pm
Herbert Norris wrote:

Dear Sir
        Please can you tell me if it is possible to charge my 12v sealed battery up with two 6v chargers -how to wire them up etc .

On March 20, 2012 at 9:02pm
Ankit wrote:


What are the effects if i can charge 6v batter with an 5v supply.
As basically my application works on 3V to 5V supply but i also have to give facility to connect 6v battery (Rechargeable). so i converted 6v output to 5V for my application.
but while recharging of 6V battery i gt 5V supply.
So it has any effect on battery Life?
battery is charge till 5 V than also my application is working because my application can work on till 3V so voltage is not an issue.

On March 25, 2012 at 7:17am
Frants wrote:

Hi there.

Very informative. What if the first phase of the charging, the constant current charge, is interrupted before phase two can begin? And then, when charging can continue again (some discharging has now occurred) phase 1 charging resumes?

My understanding is, the state of the battery will determine which state of charge needs to commence. However, since the topping charge, as you say, is sort-off a rest period, what if this rest period cannot be applied, or the constant current charge cannot be completed?

Thank you.

On March 25, 2012 at 2:41pm
Robert Kondner wrote:

Good observation. The “Interruption” you describe can fall into two situations.

  1. The battery has been disconnected during the interruption and replacement with a different battery is possible.

  2. The battery has not been interrupted.and the controller is one that monitors battery discharge.

If you have a controller that monitors all charging and discharge currents, and it operates with a VERY low battery drain (10s of ua is reasonable), then as long as the battery has not bee disconnected you retain the battery state. You can pick up a charging profile at a later time.

When battery is disconnected all bets are off. You need to assume a new battery has been connected and you need to charge and/or condition it to a known state.

I believe all battery current should pass through a smart controller. This gives you the chance to prevent over charge or over discharge with a series switch. It is not that expensive with a PIC, some circuits and a couple of FETs.

I have some small chargers at www.indexdesigns.com and I would be happy to describe what I did in the Battery Boss software.  bob at kondner dot com

Bob Kondner

On March 30, 2012 at 4:00pm
ra'ed wrote:

i went to put a specifications to buy a power system for telecommunications stations, the battery will be a 12 v 200ah four battery connected to gather in series to give the -48 vdc and a charger of the same voltage:


On April 4, 2012 at 10:02pm
Bikash kumar sahu wrote:

Plz help me, regarding for charging of a 12V dc battery, i have to design a dc dc voltage converter for 12V to 16V ? but at load condition i am getting only 200-300mA current? I it possible for charging of a battery

On April 9, 2012 at 5:09am
acc wrote:

  Can a battery be charged (eg. thru solar panels) and discharged (used for some appliance) at the same time ?


On April 14, 2012 at 12:32pm
Vic Tkachuk wrote:

I have a motorhome set up for 2 regular lead acid 12 volt deep cycle batteries,
I have the chance to buy up to 4 gel cell 12volt deep cycle batteries.  Can I safely
rerig and install 4 using the same charging set up ?  These are batteries which
were used for solar storage (Power PSG-12105)

On April 14, 2012 at 2:16pm
Robert Kondner wrote:

You did not say if your existing batteries are flooded plate or what.I assume your existing charge was purchased for whatever type battery you have.

The problem you need to watch out for is a “3 Stage Charger” often looks for the battery voltage to peak when the battery is charged. If you apply such a peak voltage to a sealed lead acid battery, and depending on the charging rate, you might generate more gas than can be internally recombined.

I looked into this PSG-12105 quickly and did not see any charging profiles, the peak voltage mentioned was about 14.1. A Three state might be looking for 14.6 or higher.

Bob K.

On April 17, 2012 at 11:07pm
Gilberto Prida wrote:

I need a replacement (lead acid) battery for a Quipp jump starter which printed information
is the following: Prostar bat.  6PS0070H - 12 V. Cycle use 14.6—15.0 V. Standby use
13.6-13.8 V. Initial current 1.75 Amp. Max. -This bat. has terminals.with holes for bolt
and nut.  I appreciate your answer and the price for this jump startert if is convenient
for this 4 year old apparatus. Thanks in advance….Gilberto

On April 19, 2012 at 11:23am
Phil Murray wrote:

Is it safe to charge a 6v 10aH with a basic 7v 2amp charger?

Thank you


On April 21, 2012 at 6:31pm
tareti kireua wrote:

Dear Sir/Madam

I use a 100N sealed batterry (12V) in my home powering three light blbs of 7watts each but I only use soler charging only and an electric charger as a backup when sunshine is not surfficient. The charger gives 14.5 max voltage but I just want to know how many hours should I chrge my sealed battery in case solar charging is not availale de to overcast or caherging is really lower than 12V.

Should I use electric charger full day or any advice from you on how to use the electric charger to avoid damage to my sealed batterry.

Hear from you


On April 23, 2012 at 10:21pm
joe wrote:

Sir,i would like to build a charger for lead acid batterys.  the one i have is a commercial one and inside theres just a transformer a retifier and an ammater.the only protection it has is a thermal switch on the tranformer.Personally i find this a bit dangerous as it does not cut the chaging when the battery emf is reached,(13.8-14.5V).I already ‘ve wired a couple of test circuits one of which used two thyrsistors,one for monitoring the battery votage andthe other is the switch.the problem i’m find with most of the circuits is that as that when i apply the charging, the voltage goes up cos the battery acts like the capacitor and this goes above the sensing voltage set ie 13.8v.would current limit solve this problem?thank you,

On April 24, 2012 at 3:24pm
costas wrote:


If you had to charge a 6V 6Ah battery, what maximum current float charger would you recommend?
Would the current output value of the charger be different if I were to use a 4-steo charger?


On April 26, 2012 at 9:50pm
Joe wrote:

Table 4-5 talks about “severe overcharge”, yet maintenance free car batteries are charged by the alternator at around 14.5V in a hot engine bay all the time. Can you explain?

On May 3, 2012 at 8:54pm
Ross Wi wrote:

Can “Negative Pulse and Burp charging” be postpone battery service life and improving battery performance & desulfation?

On May 14, 2012 at 9:40am
Raymond wrote:

I have to make a solar battery charger for a 12v,13AH lead acid battery how do I calculate the charging current required to charger the battery from a flat state in 13hours?

On May 14, 2012 at 10:08pm
HASEEB wrote:

i have two 6v 4.5ah battries. i want to charge them in series. is it ok to charge them with 12v 1250ma adapter. how long it will take to charge them fully

On May 19, 2012 at 9:05am
Tim Hellsten wrote:

Hello.  I have a question.  I have an electric scooter using a 48v 30AH SLVR lead Acid battery.  running a 500watt brushless motor.

I currently charge it with a 48v converter @ 3 A charger plugged into house power over night to charge the scooter.

I want to increase the range so I have had a thought to put a 1000 watt honda generator on my scooter and run the generator while I am driving.

the issue I see right now is that I am probably drawing more power from the battery then my 3A charger is able to put back.  I was contemplating purchasing a 48v 30A charger and charging my batteries as I am driving.

I need some assistance from the folks here. 
can anyone offer some information.  will this work?  will I blow up my batteries?
are there issues charging batteries at the same time you are draining them?


On May 20, 2012 at 9:45pm
Ian Warner wrote:

I bought a new lead acid batterry for my golf buggy, a Panasonic model LC-XC1228AP after x anount of hours the charger indicates it is fully charged, but I cannot get 18 holes of golf out of it, I contacted the supplier who sent me another one, it is the same. It has been suggested that this type of battery initially needs to be run down completely and then recharged before use.
Can you please advise me.
Regards, Ian Warner.

On May 21, 2012 at 6:13pm
Bob Kondner wrote:

That is only a 28Hr battery. I know nothing about golf cart loads but 28Hr does sound like a lot. What does the golf cart motor require?

I checked, it is an AGM battery. Do you know for how many hours it took how much charge?

No, You do not want to run it down all the way, very bad idea. Just be sure you charge it all the way. To do that you need a volt meter and the specs from the manufacturer.

Bob K.

On May 21, 2012 at 11:53pm
Ian Warner wrote:

Thanks for that info Bob K. It took approximately 3 to 4 hours to show fully charged on the charger. I put a voltmeter across it and it read 13.45volts. The info off the buggy motor is 12 volt 180w. This size battery was supplied with the buggy when bought new. I have used the battry four times now and each time it seems to be getting stronger. I can now get 18 hole out of it, although still quite weak at the end. Once again, thanks for your help.
Ian Warner.

On May 22, 2012 at 12:55pm
Bob Kondner wrote:

  If the charger only took the battery to 13.4 V then the battery was not fully charged. I would guess you are using a “Float Charger” which uses a very low vlotage as to not overcharge. You want to see the voltage head closer to 14.4 if the battery is < 70F or to 14.2 if > 70F. At 100F only 14.0V. AGM are not like floated plate, you don’t see the voltage rise up as much at the end of charge. You need a charger with some smarts.
Bob K.

On May 27, 2012 at 7:34am
ryan wrote:

what will happen if electrolite was added to lead acid battery

On May 31, 2012 at 2:56pm
Kiel Durmaj wrote:

@Ryan, All lead acid batteries have electrolyte (hence the term “acid”). You may be referring to AGM batteries which are also referred to as acid starved batteries due to the limited amount of electrolyte.

If this is the case, it is never recommended to add more sulfuric acid to the battery since the concentration/level from the original fill is great enough. Since it would seem have a SEALED lead acid battery and it would only damage that seal to open it enough to add any form of liquid. That being said, don’t open your battery.


On June 2, 2012 at 12:11am
mathan wrote:

flooded battery revival works not suitable why?

On June 8, 2012 at 4:39am
maulana wrote:

how long does a 75 watt solar pannel charge a 120 ah Raylite maintainance free battery, that is 50% full.

On June 21, 2012 at 12:03pm
Sunil wrote:

How to set up a Float voltage on a charger ? Do I need to isolate Battery set or I can set up with Battery set connected ??

On June 23, 2012 at 3:52pm
Clive Pearson wrote:

Hi   I have 3 batteries 12v @ 220Ah wired in Paralell what charger and at what amps would I need to recharge these ,these are for a camper van system

Also a 24v system = 2x12v @220Ah in series same question as above

One other question I know with ohms law if you increase the voltage of a supply you drop the amperage and visa versa if you drop voltage you increase amperage.
What happens in a battery in series as regards the Ah as in for example 2x12v@220Ah in series = 24v as there is a voltage increase does this drop the output amperage regards clive

On July 9, 2012 at 10:38am
Ron Gardner wrote:

I have a vehicle with 225 amp alternator charging a 150 AH battery. When battery level is low (11.8 volts with no load) & I start engine & measure the current from alternator charging battery I get around 45 amps? If I add a 45 amp load the alternator output goes to 90 amps, why does the battery charging by itself only charge at 45 amps? Is there a limit on charge rate that lead acid batteries will charge at?
Any insight would be appreciated.

On July 9, 2012 at 11:13am
Bob Kondner wrote:

  There are a LOT of reasons that you don’t get more than 45 amps. The alternator is not a “Zero Ohm Impendence Output”. If you short out the alternator you might get 225 Amps but that must be one heck of an alternator. The alternator output is not like a regulated DC supply.

Plus you have resistance in wires and the battery.  You might want to check voltages at various spots and see where you are dropping any voltage due to wire resistance.

Yes, there are limits to charging rates but that depends on the type of battery. AGM batteries spec very high charging rates but I have never experiments at 100 amps or more. Flooded plate batteries exhibit a sharp increase in voltage as they are charged. The only way to get “100%” capacity, or at least a high level of charge, is to allow the battery to charge up slowly. Getting that last level of charge takes a long time.

Bob K.

On July 20, 2012 at 10:04am
john Bean wrote:

What is the best battery charger to charge a 48v (4-12v 14amp) system? Is a 48v 3.0amp charger sufficient to fully charge them?

On August 5, 2012 at 10:10am
Danilo wrote:


i have at home Pb battery 100Ah 12V. Im charging these battery with 5,0 A and i have setup charger with 2,25V/cell. Is these good?
Link for these battery M83CHP12V27

http://www.tpscrail.com/products/gnb/PDF/Element Bloks.pdf

On August 9, 2012 at 12:07am
Kein wrote:

Dear sir,
How do I calculate a battery recharge time so as to ensure it is less or equal to 8 hours for my design below?

I designing a PV system for a 4w transmitter to operate 24 hours per day, 5 days of autonomy, battery losses of 0.85, Depth of Discharge of 75%, nominal battery voltage of 12V DC. I have calculated my battery capacity (Ah) as follows:

(4x 24 x 5)/(0.85 x 0.75 x 12) = 63Ah.

I have also calculated my PV size as below:
Peak power Wp = (1.25 x Transmitter Load x Daily duty cycle)/(Peak Sun Hour)
Wp = (1.25x4x24)/4.2 = 29W ~ will peak 30W 12V mono crystalline panel Isc =18.3A, Voc =20.7V

On August 14, 2012 at 3:38am
Lawrence Coomber wrote:

Can anybody help me with this one.

I have 25 x 12 V 150 Ah Gel Cell Batteries connected in series showing about 320 V output.

I have the series battery bank connected in parallel to a solar array with a constant daily Voltage output of about 330 - 350 V.

The circuit includes a blocking diode between the battery bank and the solar array to prevent reverse current from the battery bank to the solar array.

The circuit is connected to a varying domestic home load. Obviously at night the battery bank is the sole source but in the day the solar supports both the load and also the battery re-charging.

Am I correct in my analysis of this circuit? I have tried to create a simple “balanced” circuit here with minimum of complexity of seperate cahtgers which would not be available because of the series circuit anyway.

Thank you for any commects you can offer.

On August 15, 2012 at 8:04am
sureshkumar wrote:

Iwand install 24 volt ,1kw,dc power in offshore crane72 houre battery back up.crane enginhave 24 volt 30amer battery charging altrenaterr.can you give an idea?

On August 18, 2012 at 11:44am
Baruah wrote:

Is it dangerous to connect a small UPS with a big 150 Ah tubular battery? The ups transformer gets very hot within 15-20 min of charging, but with some improvised cooling aid I keep it going. And how the internal resistance of LA btr changes with charge or discharge?

On August 21, 2012 at 10:40pm
F J Husein wrote:

I was wondering if anyone could help me.  I have 4 12V Lead acid batteries connected in series to my IPS (Instant Power Supply) unit.  The connection between 2 batteries got snapped.  Now I have 2 questions. 
1.  I disconnected the wiring to the positive terminal of the 1st battery so is there any current flowing through the other connections?
2.  How do I rewire the whole system so that it is up and running again?

On August 22, 2012 at 12:32am
venom wrote:

@ F J Husein

so you have a 48V system (12V battery X 4 in series)

1. this is a chain of battery, an open in this chain means no current flows through any of the battery.
2. wiring  
              +      -  c   +      -    c   +      -    c   +    -
            48v                                                 0v
            to IPS positive                                     to IPS negative

+    -  indicates one battery
‘c’ indicates a connection between - and + of adjacent batteries

On August 31, 2012 at 10:31pm
Deepthikumar wrote:

how to calculate the amount of active material for a lead acid battery based on Ah?
how to calculate the SOC using OCV? what is the relation between SOC and specific gravity of acid in lead acid battery?

On September 1, 2012 at 4:44am
Muhammad Farooq wrote:

How much current per hour required for 150 Amp Lead Acid Batteries

On September 16, 2012 at 5:23am
Alex wrote:

Hy, I have a car battery rated 12 V, how do I know the level of how charged is ? From the voltage ?

On September 26, 2012 at 9:10pm
Roy McSheffrey wrote:

Is it possible to have my battery charger running at the same time that I’m running an ac adapter to power my computer,

On September 27, 2012 at 6:22pm
ling michael wrote:

How many % or cc water loss of maintenance free battery during service life, please give me data or water loss curve. thank you.

On October 9, 2012 at 7:00am
Shan Mehmood wrote:

How much charging time can we take a 12 volts, 190 Amp Lead Acid Battery to charge properly using 26 Amp and 12.80 volts charger?
And after charging completion, how much should the battery voltages?

On October 10, 2012 at 12:30am
James Japp wrote:

Some time ago generator died on my old diesel truck, so I have to recharge the two SLI batteries manually (I’ll install an alternator and scrap the stupid generator). The charger that I have is a simple 12V 20A unregulated unit, so I put a digital volt meter across battery terminals and monitor voltage and here I noticed something strange.

After some 30 minutes or an hour voltage reaches certain point between 13.85V and 14.10V and stays there for an hour or longer. Current is also stable at about 5A or more (I got two 66Ah batteries in parallel). Batteries don’t get warm during charging. When I disconnect the charger and continue charging after 10 hours or so it immediately goes over 14.4V or so, no matter whether I left it sit for more than an hour at the same voltage or whether I disconnected it much earlier.

What is going on here? It looks like batteries are just dissipating power somehow, but how’s that possible? How can batteries absorb 2-3A each and keep the same voltage that indicates that they are not yet full and then after some rest period ‘become full’? They are not too close to the engine, so while the truck is running they get to about 25-30°C (77-86F) and overnight they cool to about 15-20C, so I don’t think that the temperature is important factor here.

On October 10, 2012 at 12:47am
James Japp wrote:

@Shan Mehmood

You can’t charge 12V battery with 12.8V charger, that voltage is nowhere near enough to charge a battery.

But I don’t think that you have a 12.8V charger, I’m guessing that you used a digital multimeter and measured voltage across charger terminals when it wasn’t connected to a battery. Digital multimeters (DMM) get confused with pulsed DC and most battery chargers of that size don’t have filtering capacitors (because they don’t need them). DMM tries to read an RMS value of full wave (or half-wave if you charger is very old) and fails. Anyway, RMS voltage is not important value for a battery charger, you wan’t to know it’s peak voltage and to measure that you need an electrolytic capacitor with voltage rating of at least 25V. You need to connect it in parallel with your DMM and charger (don’t mix the polarities) and then read the voltage.
For example, when I measure my charger with DMM it has 12.00-12.20V (it depends on mains voltage which fluctuates in my area), but actual peak voltage is 18.20V.
You don’t actually need to do all this, but you can if you’re interested.

Now to answer you question - no one can tell you how long you need to charge a battery because that depends on many factors - how much have you discharged it, not all batteries charge at the same rate, some take longer and charge current and voltage depend on your mains voltage. So, connect the charger and monitor voltages, for a full charge at room temperature voltage should be 14.2-14.4V, you got more details in this article.

On October 11, 2012 at 1:04am
Wilfred Kube wrote:

I have a Toyota Coaster bus which is fitted out as a motor-home.  The vehicle was manufactured with a 24 volt electrical system, which uses two batteries in series, of 12 volts each.
I have outlined a description of the auxiliary electrical system below, but my basic question is, how can I know how depleted my auxiliary batteries are at the end of a day in which the refrigerator has been working for a long time?
I think the basic rule is that the batteries should not be discharged below 50% of their capacity, but what reliable method can I use to determine when they have reached this point?
There are two auxiliary 12 volt batteries in series, each 120 amp-hour, to provide power for the “house system” – namely refrigerator, lights, water-pump, and various 12 volt power outlets.  The refrigerator is the major user of battery power, because it is a compressor fridge which uses the equivalent of 12 volts 8amps (i.e.96 watts) while it is running, and it runs for approximately 8 to 12 hours in each 24 hour period depending on how hot the weather is.
The auxiliary batteries are charged by two solar panels of 80 watts each, and receive additional charging from the vehicle alternator when the engine is running. There is a battery isolator which automatically disconnects the auxiliary batteries from the vehicle electrical system when the engine is not running.
The voltage regulator for the solar panel charging system provides a constant display for the auxiliary system, including the auxiliary battery voltage.  I have been in the habit of checking the voltage last thing at night, and first thing in the morning, to find how much power the fridge has taken from the batteries.  If the night time voltage is below 24.8volts, then the morning reading is below 24.0 volts.
The problem is that if we have not done much driving on a particular day, and the solar panels have not done much charging because of cloudy weather, the night-time voltage may only be 24.2 volts, and the morning voltage not much above 23 volts.  If the battery is at 24.2 volts when the fridge is not running, then when the fridge starts running the voltage reading drops down to about 23.5 volts.
And so my question remains, what is the lowest acceptable voltage for my auxiliary battery system, so that the batteries are not damaged by being discharged too much.
Thank you for reading through a long and detailed letter, but I wanted to provide sufficient background information.

On October 13, 2012 at 1:54am
Graham Budd wrote:

I have 6x2v full traction batteries linked to give 12v and 860 amps at c20’ my question is how long should I set my charger to run for at bulk, should I set the absorption charge at 14.8. Or leave it at 14.4 volts? My charger is a victron Phoenix multi 2500/12/12v
Thanking you in anticipation

On October 19, 2012 at 1:31am
Kiani wrote:

I have a 12v lead-acid battery that charges to 16.65v when fully charged. why does that happen?

On November 7, 2012 at 1:25am
Patrick wrote:

What do you mean by Cycle use voltage = 14.4-15 Vdc and Stand by use voltage = 13.6-13.8 Vdc located at the battery specification.. When the UPS is running may know what is the standard voltage charge of each batteries.

On November 10, 2012 at 2:24pm


On November 14, 2012 at 6:17am
David wrote:

I have been using a charger to charge a SLA Battery 12v 21ah,i have put the charger through a charger tester to show the v and ah of the charging cycle,should the voltage have peaks /spikes during charging?

On November 17, 2012 at 10:16am
Lutz wrote:

I have 2x 12v 90Ah gel batteries in series to give me 24V. My load is drawing 0.7A. I am using 2x 130Watt 12V solar panels in series to keep batteries charged. The charge current from the solar panels at midday ojn a full sunshine day is 2.5 A.
It seems my batteries are runnig flat in about 12 days.
I dont seem to find the problem, please help me to solve this problem.

On November 19, 2012 at 4:06pm
Jorge Viana wrote:

Please help me:

We’re building a small solar plant to serve an isolated community within the Amazon jungle. We are using VRLA batteries. How much thermal energy is generated in the charge cycle? Total energy stored 60kW.


On December 1, 2012 at 12:35pm
Merle Frey wrote:

I have a 12 volt Schuyler battery charger if I connect it to a discharged 12 volt battery,  I get on the meter a green light then it goes to 15 amp charge then back and forth from green light to charge. What is causing this to happen These are both marine batteries. but it doesn’t matter if I put the switch on Normal or Marine.  Thanks

On December 2, 2012 at 12:06pm
Ron Kushnier wrote:

I need a Float Charger for my 12 volt car battery.  What I have is a fairly sophisticated Craftsman Ni-Cd battery charger (Mod # 974062-001) for an old electric drill.  The 1 hr charger says it works for 12.0, 13.2, and 14.4 volt batteries.  I measured an open circuit voltage of 30 VDC coming from the charger.  When I attach my car battery to the charger, I see 12 V across the terminals with a constant 60 mA being pumped into battery.  My question is whether 60mA represents enough current for a trickle charge, or am I just powering the clock and other electronics of the car with the car power off.

Thanks in advance.

On December 7, 2012 at 9:03pm
Fred Robson wrote:

deer sir ,

what means it to charge a battery?

On December 14, 2012 at 7:03am
Hugh Leekie wrote:

Some help, please?  I ave a 6V 1.2Ah sealed lead acid battery which is part of our house alarm and which is charged via solar panel. What with the poor summer and now very short light days it is requiring a top up. I have removed the battery from the appliance and am charging it with a charger 6V dc 500mA 3VA.  The battery was showing 4.6V with my digimeter before charging started and now after about 40 hours of charging it is showing 5.75V.  Is this a normal situation—should it take as long as that?  I would welcome some guidance please as the source of the house alarm kit suggests charging at 7.5V 500mA whereas the shop selling me the charger says charge at 6V and that is what the charger is doing (hopefully).  Thank you.

On December 14, 2012 at 7:46am
Ron wrote:

I would check the open circuit voltage of your charger with your meter.  Hopefully, it would be somewhat higher than 6 VDC. Otherwise when it is under load from the battery, it will not be able to pump enough energy into the cells. Also, you may want to change your digimeter to read amps, put it in series with your charger and battery and check the current being drawn during charging.

On December 14, 2012 at 8:56am
James Japp wrote:


Cheaper digital multimeters can’t read the voltage accurately on pulsed DC, which is what most chargers produce. Usually DMM will show lower voltage. It’s best to connect the ammeter in series and to see if the charger is charing the battery. For your application charging current should be at least about 50 mA, ideally around 300 mA, but not higher than 360 mA. OCV of a charged battery should be 6.3V and the voltage on while charging should be 7.2V. 5.75V is a lot lower than it should be. If charging current with that charger of yours is several hundred mA you most likely have dead battery, if charging current is low then your charger is inadequate.

For this kind of battery you could use any cell phone charger, if you could find a way to connect it.

On December 15, 2012 at 6:27am
Hugh Leckie wrote:

Thank you Ron and James for your words of advice. Whilst connected to the charger and charging I put the digimeter terminals across the battery and the reading was 6.5V.  The “bare” battery still only is showing 5.7V so it looks like the battery is on the way out. Time for a replacement. (Incidentally putting the DMM terminals across the charger unconnected leads whilst switched on and set to Dc voltage 20, there is no reading-the red charging light does not illuminate. It does however light when the leads are connected across the battery terminals.

On December 19, 2012 at 8:00am
Denton wrote:

I have a problem with battery . I use a 6 cell 12 v lead acid battery with an inverter for uninterrupted power supply. I didn’t do any maintainance on the battery for a long time and recently I found that plates in all the six cell were exposed .I have since filled the cells with water .Battery seems to be working but find that its temperature while charging goes beyond 40 degree centigrade.I am wondering if this is normal .I remember reading in the article that normal is around 30 degree .I can say ambient temperature is about 25.

On December 19, 2012 at 9:55am
Bob K. wrote:

  First I hope you used distilled water, right? grin

Some info required:
  AHr rating of the battery, obviously a flooded plate
  Nature of charger. Smart? Number and description of charging cycles.

What level of charging current do you see and at what voltage?

If the plates were only slightly exposed I would not expect a lot of damage. If we are tolking 50% of plate exposure well that would be bad.

I worry that if you had a lot of exposed plate perhaps you effective battery capacity has been sriously reduced. So now your charger is effectivly charging a much smaller battery. Once a battery warms up it’s terminal voltages tend to drop. If you charger is in a bulk phase and the battery voltage stays low the charger could stay in bulk mode. If the charging current is high you could end up in a thermal run away situation.

You need to watch the battery termina voltage. If it is not hitting about 14.4V when it should be reacing full charge *23C) then you have a serious battery problems.

Bob K.

On December 24, 2012 at 9:24am
Jerry Marnie wrote:

I have a dozen 6-volt golf car batteries that charge up to about 6 volts each, and drop only about 0.3 volts when tested with a load tester. However they each continue to draw maximum charge current when connected to a variety of chargers, and do NOT charge to at least 6.3 volts, as my other batteries do. Some have normal specific gravity, and some are low.

Is there anything I can do to recondition these batteries??

On January 6, 2013 at 4:17am
abrar wrote:

hello every one i am student of 10th class i have no source to study continue please let me how i made a battery of 4v 0.5Ah thanks in advance.

On January 13, 2013 at 10:54am
Hasnat Jamil wrote:

i have a 12V lead acid battery. It is used for a inverter used for uninterrupted power supply.
-after one year use it is now unused for almost one year(no charging and watering).
-it has voltage 6.28V(measured by DMM) and plates are exposed about one inch.

*what should i do to recover it???

On January 14, 2013 at 2:04am
Hasnat Jamil wrote:

can i put Distilled water in it and charge it with a trickle charger???

......pls anyone grin

On January 15, 2013 at 5:53am
Mithu wrote:

Hello every one
i am charging 12V ,4.5AH   lead acid battery ,and charging up 13.8Volts and recharge the battery if below 12.9Volts , but after fully charged to 13.8v it well recharge again i.e floating charge fully complete charged   and charging

On February 8, 2013 at 3:26am

plese send my Email 12 volts dc to 220 AC output, without transformer circuit diagram

On February 16, 2013 at 1:20am
Batte Ryman wrote:

On January 13, 2013 at 10:54am
Hasnat Jamil wrote

I think that battery is sulfatised. So in my opinion you better buy a new one.
Not much choice.

On February 16, 2013 at 8:34am
Batte Ryman wrote:

Hugh Leekie
On December 14, 2012 at 7:03am
On December 15, 2012 at 6:27am

You talk about sealed lead acid, part of house alarm, equipped with solar panel.
House alarm means: there is almost always grid power available and I assume the alarm actually is connected to the gird, with the solar panel purely as backup power source.
My understanding is that this battery will (or at least should) be in float charging modus for almost 100% of the time. And that with proper float charging (at always the correct voltage with respect to its temperature) such a battery could last for 10 years.
If the system is much less than 10 years old, then either the float charger should be inspected and repaired/replaced/improved, or my assumption about the grid connection is false. In either case the battery should be replaced, because as you can read here:
http://www.progressivedyn.com/battery_basics.html the voltage should not have gone below 5.25 V in order to have prevented serious damage.

On February 25, 2013 at 4:42am
aswin kumar wrote:


we are planning to use 54Ah battery, so i would like to go with constant voltage charging, i have a source of 14V @ 7A but it is the source to all other circuit also. so is it recommended to charge a battery with the same source and more over what will be the intial currnet to charge the battery whether is it calculated by 2C. if it is 2C then main source is loaded and will there be a drop across the volatge.

On March 3, 2013 at 11:28am
Rich wrote:

I am wondering what happens if one accidentally charges an LSI battery with a “deep cycle” charge?

I was using a 10 amp 12v charger on ‘automatic’ setting but set on “deep cycle” instead of LSI. would this ruin my battery or make it otherwise unable to receive a charge?


On March 7, 2013 at 6:25am
muhammad arshad wrote:

hi ,,,here is some dangrous with me last few months i bought a new 200 ah battery for my ups ,,,first two month i did not felt the put down water in the battery that was full and cool that i saw my battery started to dry water suddenly and some heating .... i put the water after two weeks i felt the back is just 30 minutes on 100 watts usage .. i checked the battery that was tooooooo hot and there was no water inside ..... i put the water in it…............... and googled   there i found that my battery was sulfated   i desulfated it ,,,first of all i drained all acid inside , and then washed with water   ,,then i put baking soda for many hours in it then drained baking soda water ...then put epsum salt in it   with water and put it at slow charge after 15 hours charging   battery was cool then i put the 50 watts load on it ...back up was just for 20 minutes   .....now i am charging it again at slow current just 10 volts and 7to 8 amp but the backup is till now just 20 minutes ... now i am worry what should i do now can i put sulfuric acid and water mixture in it what should i do pls help me thnx   email is     alpha_19_20@hotmail.com

On March 12, 2013 at 4:44am
sc00by2 wrote:

Very informative page, thank you!

I have a question for you. Using a dc to ac converter connected to a 1700mah lead-acid battery, will I be able to charge a laptop battery that draws 120-watts, and how many of these could I charge?


On March 13, 2013 at 1:41pm
James Japp wrote:

First of all capacity in amp-hours does not give you the total amount of energy stored in that battery, you need to multiply that with (nominal) voltage. For example 12V, 1.7 Ah battery has theoretical capacity of 12*1.7 = 20.4 Wh (Watt-hours).

Label on your laptop charger says 120W which is the maximum power it can draw, it doesn’t draw that much all the time.

Laptop batteries typically have capacities between 40 and 60 Wh, so its two to three times more than 12V 1700 mAh battery, so you probably won’t be able to charge the laptop battery. You could be able to run the laptop (with its battery removed) from your lead acid battery and if your LA battery is 12V one you could use car adapter for your laptop which is probably more efficient than DC-AC inverter. You’ll probably need a lot bigger battery though

On March 22, 2013 at 7:57am
suresh vishwakarma wrote:

a lead acid battery bank having normal voltage of 110 V is to be charge using DC source 160V from initial voltage of 1.8V/cell. Each cell of the battery has internal resistance of .02 ohms battery is being charge up to boost voltage of 2.4V/cell. charging current at a beginning is 5 AMP. What will be current at the end of charging. Draw the circuit diagram of charging circuit showing the value of series resistance used.

On April 12, 2013 at 1:28am
Saurabh wrote:

I have a 12 volt 7.5 Ah battery and i want to charge it with a solar panel of rating 25 watt 21.50 volt and 1.59 ampere….can i connect it directly or do i need any special arrangement?
Thanks in advance

On April 12, 2013 at 8:38am
Bob K. wrote:

You definitly need a means to prevent overcharging. You small battery will be highly over driven by your soloar panel. There are a lot lof low cost solar charger modules that will do this for you.  Also, your panel output (1.59 A) is a little high for charging though a charger controller should take care of that. You might get a premature “Full” state during full sun which would leave your battery at less than 100% (80 or 90%).

Bob K.

On April 12, 2013 at 11:15am
Saurabh wrote:

But the max battery charging current is stated as 2.20 amps…is it necessary to have a charge controller or any other things like transistor or opamp can be used…
Thanks for your reply bob
I am a newbie In this field and also dnt hv sufficient funds for charge controller is there any substitute for it

On April 12, 2013 at 11:32am
Bob K. wrote:

I assumed, perhaps in error, you had a lead acid of some type. A charging rate of C/20 is nice, C/10 would be ok, but I think you said this is a 7.5AHr batter? 2.2A charging is quite high depending on the battery type. Do that on a sealed gel battery and you will destroy it. Do it on a flooded plate and you will generate a lot of gas and go through water quickly.

You can reach me at “bob at kondner dot com”, let me know what kind of battery you have.

But in general yes, you need some type of charging controller. That will include a voltage reference, op amps, transistors and so on. You can take a look at www.indexdesigns.com for some of my items. These are positioned towards smaller batteries like what you have.

Also, don’t neglect software. These little units I have include maybe 5K line of PIC assembly code. Hand written in assembly, very tight, hard to write. Pull down some data sheets and take a look for some ideas.

Bob K.

On April 13, 2013 at 4:16am
Saurabh wrote:

Sir it is a sealed lead acid battery….with 12 volts 7.5 Ah and 2.2 ampere as max charging current

On April 13, 2013 at 6:29am
matt wrote:

Hello there, I have two 12volt sla batteries one of 12 amp hour and other of 4.5amp hour. i use them for my little audio amp as it is 12v. I Use a solar panel rated as 17,5v at 30w, am i ok charging both batteries at the same time as it is still charging a 12v battery but of the added amps of both batteries at 16,5 amp? all the best matt   uk

On April 19, 2013 at 3:43am
nikhil wrote:

      i have 12v 600mAH battery. during charging the voltage and current of charger (using lm317) is 14.4 V and 200mA. i used to charge the battery without changing voltage till the current reduces to 18 mA(around 3% of total capacity). the battery shows a max of 14.24v at a particular stage of charging process . i want to know whether my charging method is correct or not. please help me . . .

On April 19, 2013 at 3:51am
nikhil wrote:

      sorry , i forgot to add charging time. my charger took around 6 hrs to charge the battery .the charging rate is c/3, but it doesn’t make any temperature variations ,that’s why i use this charging rate .

On April 19, 2013 at 4:09am
aswin kumar wrote:

hi nikhil,

you are charging with a constant voltage for 2.40 per cell initially which is ideally charging voltage for fast charging, 14.24v drop from 14.4v is my question why it has dropped more over your charging is in toppping charge which you have to leave it for some time. The best was to find your battery is fully charged or not is connect a load acros the battery and measure the voltage it should be approximately 2.12per cell which is 12.7V approx. And also confirm with the graphs in battery datasheet on constant voltage charging


On April 22, 2013 at 12:03am
nikhil wrote:

hi aswin,
          first of all thanks for your valuable comment . during charging the battery voltage never exceeds 14.24v. when the battery is allowed to charge for some more time the battery voltage starts reducing .i am using lead acid battery and it is 1 year old. when i connect load(50 mA) after charging , battery voltage will 12.6 or12.7v. since the load is 50mA it should give backup for 12hrs, but the backup is around 5hrs(till 11.9v). that’s my major problem .
thanks & regards

On April 22, 2013 at 3:54am
aswin kumar wrote:

Hi Nikhil
if the battery voltage is 12.7V then it means the battery is fully charged, your minimum discharge voltage on light loads can be 1.75V/cell which is 10.5V approx for six cells lead acid battery below which it should not be discharged, we can discharge upto 10.5v only, kindly refer to your battery datasheet for the tabular column of the discharge volatge.


On April 23, 2013 at 12:09am
nikhil wrote:

hi Aswin,
now i am getting around 8 hrs backup . when i searched about charging in internet , the minimum discharge voltage on most of the sites was 11.9v. that’s why i used that voltage . aging might be the reason for the low backup time .
thanks and regards

On April 23, 2013 at 11:56am
Kelly wrote:

Hi, I have 12 2.2 v batteries in a series as backup for my solar system. I have not once been able to get the batteries up to their specific gravity, once even having to ship them back to the dealer for a full charge. We have increased the charging set points and extended the absorb charge period to no avail.  I am charging them with a generator putting out 120 amps and charging them at 30.0 volts. Do you have any ideas? Thanks so much.

On April 23, 2013 at 2:20pm
Mark wrote:

I have an old acuscope B which has 2 sets 8 batteries wired + to -  .  Cyclon lead acid 2 volt 2.5 Ah batteries. The way they are wired into the box is as 2 separate 16 volts coming together as one at the on off switch. Any idea what volt/ amperage I need. I was told 40 volt, 200 mA, but that doesn’t seem quite right. It has a very old small transformer, but all the writing is gone 30 yrs. ago . Thank you!

On May 21, 2013 at 6:24am
Viktor wrote:

I’m preparing to do the initial charging on a FIAM SDH 17 battery, 640Ah. Manual states that it should be done with 2.7 V per cell, 0.10C10 (64A) ought to be the limitation for charging curent and this should take 15-16 hours, so that, at the and of proces, 1.5-1.6 times capacity of the battery should be delivered. I don’t have axpirience with this kind of work but some of my colegues had problems with high temperatures, gasing… Let me add that I’m in Nigeria so temperatures are higher. Does anybody have some suggestions? Should this charging be done with open cover, because of the presure building up in the cell? Thank you!

On June 2, 2013 at 10:36am
derek wrote:

hi im new to the solar scene i have hooked up 8, 245w 52 voc panels in parlell to a 80v max in mppt charge controller i have 8 6v 220 ah golf cart batteries (it doesnt say at what amp the amp hour drain is at) wired in 24v with one string. this bank i sort of stabbed in the dark with and is way under powered.

Q i was trying to use the bank as a buffer as i have a grease car i was trying to use as a generator to top off with beig a 24v system and a 12 v altenator i was wondering if i could tap into the in on the charge controller side to boost the incoming voltage 52 panels +15 on the car. toget 67 ish as i understand i will still get some high voltage on cloudy days but supplement some amps from the car as the panels will drop off right?

Q can i put a diode in line to protect my car from high voltage when connecting to the panels ,will the cars 60 amp current hurt the panels , will the current leak into the panels as it would be cloudy , will my voltage regulator on the alternator be stressed ?will this scheme not likely work? thanks

On June 13, 2013 at 2:52am
Kosta wrote:

Hi everyone,
I own a velotaxi and use 2 sets of lead acid batteries (not connected). Each set is 4x12V. The “small one” is 12V, 18Ah cheep chinese batts and seems that the cheepest chinese charger works not bad and charge it but “the big set” not really. The big one is 4x12V, 42Ah Varta B35, 2 weeks old (might not be very good choice ). I want to buy a good charger in the low-middle-middle+ price range. Any advice about type, brand, specific model is very welcome and highly appreciated.

Kind regards,

On June 13, 2013 at 3:17am
Atu Ben wrote:

(1)Pls i have a brandnew Shoto 12v 100AH VRLA (6-fmx-100A Model) battery i want to use with an inverter for backup during black outs. Battery Terminal Currently reads 12.70v with no load
(2)I also have a transformer type charger rated 6amps 12v DC but reads 19v on the digital meter with no load on the charger terminal.
(3) thirdly i have a BNOS Electronic - Stabilized power supply rated 12Vdc/25Am but reads 13.7V at the terminals with no load

Que: (1) How can i tell with my multimeter if the battery requires charging?
      (2) Can any of the chargers above be used to fully charge this battery when is  
          fully discharged?
      (3) How many hours each would each of the chargers use to fully recharge the
      (4) What is your recommended maintenace plan for this battery if not in use for
          about a month?
Thank you very much.

On June 17, 2013 at 12:04am
Quang Dzung wrote:

What is different between charging Lead Acid Battery and Lithium Ion Battery?

Can we use the same Charger to charge both batteries if they have the same voltage and ampere rating?


On July 6, 2013 at 11:28am
David wrote:

Hy! If you have 30 minits ore one hour pause is it good to charge battery, ore is better to leave battery and continue to work after pause?

On July 11, 2013 at 12:06am
Md. Talat Mahmud wrote:

Hi, I’m an Engineer(Mechanical) working in battery factory as an Executive (Research & Development).

During charging the automotive plate, we found some extra material of white color at surface of the positive plates, i need what is the cause of that happening please suggest me.

is there any prevention or cure??

On August 15, 2013 at 11:50pm
nick rees wrote:

what is the maximum current when charging a lead acid 12v 3.2 aph battery from a 12v power supply secondary output12 v and 240v supply.

On August 28, 2013 at 3:19am
Tony Igbafe wrote:

Can a loosed batery contact cause battery to be bloated? The battery is a VRLB type and is used in a telecom site. Please your swift response will be appreciated. Thank you!

On September 4, 2013 at 4:41am
Andre Van den Wyngaert wrote:

A gel lead battery 12V 6.5Ah takes approx. 2A as max charge current. So a 3Ah cell would take approx 1 amp as max charging current.
The same 12V battery needs 14.8V for a topping charge. So to charge it, you need a 14.8V power supply with a built-in current limiter of max 2A, or lower. Most standard mains adapters don’t have such a built-in current limiter. So even if you were able to find a 14.8V adapter, it will deliver too much current and get damaged.
If you connect a standard 12V DC adapter to a lead battery, it won’t charge. Your need the 14.8V to reach topping charge and keep te battery in good condition. 13.8V will also charge the battery, but will cause degradation (due to sulfatation) after some charge cycles. If you don’t have a real lead battery charger, you can use an inexpensive lab power supply, and set the output voltage to 14.8V (half of it for 6V batteries) and current limit to e.g. 1 amp, or 2 amp if you need quicker charge. You will see that the current will limit, and the voltage will slowly rise during the hours. At 14.8V the voltage stays there, and the current will start decreasing. When it is decreased to approx 50mA (0.05Amp), disconnect the battery; it is full. At that point, you can also set the power supply to 13.8V (6.9V for 6V batteries) and keep it connected to keep the battery full and avoid self-discharging.

On September 4, 2013 at 11:43pm
pavan wrote:

In my project i am using 6v, 4.5Ah lead acid battery,
i have to stop the charging when my battery charged 100%, how would i know the battery is 100% charged or not.
when full charged condition how much voltage will get at the battery terminals.

On September 5, 2013 at 12:40am
Andre Van den Wyngaert wrote:

Hi Pavan,
If your charger puts the required topping voltage on the battery terminals, and your current has dropped to 100…50mA, I’d say it is full. The topping voltage depends on the battery and the temperature, but for these small Gel cells 7.3V is safe. Don’t apply that voltage forever, but stop charging when the current has dropped to 100…50mA. If you want to keep it connected you have to lower te voltage to 6.9V.
About full charge voltage, that depends on the battery again. Some say 6V is empty and 6.5V is 100% full. But if you test right after charging, the voltage is higher; you need to give it some time to settle.

On September 5, 2013 at 2:42am
pavan wrote:

Hi Andre,

Thanks for your response, i charged the battery upto 7.4v here the current dropped from 100mA to 50mA as you said.
if i dropped the voltage to 6.9v, then how much time it will take to full charge the battery and how much current it will take. i am charging the battery through a solar PV panel and i am using the control circuit program to maintain 6.9v.

On September 5, 2013 at 3:01am
Andre Van den Wyngaert wrote:

Hi Pavan,
6.9V is “float voltage” for maintaining the full charge; you can keep it at 6.9V forever and it will stay full. If your current has dropped to below 100mA at 7.4V the battery is full already.
If I’m right you want to charge it with 6.9V and not 7.4V. That will work, but will take longer time. The current will be lower. If it is empty at the start, the current can be 2 or more amps but will very quickly (within less than a minute) go below 1 amp. This is a “safe charge”, but can slowly degrade the battery over time since internal sulfatation can occur. But I have done this too and it has worked for years… Maybe a topping charge now and then could compensate for the sulfatation; I’m not sure of that.

On September 5, 2013 at 4:33am
Andre Van den Wyngaert wrote:

Hi Pavan,
6.9V is float voltage for maintaining the full charge; you can keep it at 6.9V forever and it will stay full. If your current has dropped to below 100mA at 7.4V the battery is full already.
If I’m right you want to charge it with 6.9V and not 7.4V. That will work, but will take longer time. The current will be lower. If it is empty at the start, the current can be 2 or more amps but will very quickly (within less than a minute) go below 1 amp. This is a safe charge, but can slowly degrade the battery over time since internal sulfatation can occur. But I have done this too and it has worked for years… Maybe a topping charge now and then could compensate for the sulfatation; I’m not sure of that.

On September 5, 2013 at 10:46pm
pavan wrote:

Hi Andre,
Thanks for your superb explanation regarding the battery charging, i had finished my battery charging task in my project but i have to test it.
i am using 6v 4.5Ah lead acid battery Battery, in how many hours it will be discharged when i am using 2watt load for FULL battery.

On September 5, 2013 at 11:08pm
pavan wrote:

Hi Andre,
i have one more doubt,at which voltage i have to turnoff the load from 6v lead acid battery for maintaining the battery efficiency(Mean how many years can i use that battery for the 2watt load).

On September 6, 2013 at 1:20am
Andre Van den Wyngaert wrote:

Hi Pavan,
if you mean: how long can I use the battery when I charge and discharge it regularly: I cannot tell. I use such a 6V battery in a flashlight and it still works for over 4 years now. I use it until the light becomes lower… then charge it again. Load is 750mA.
If you mean: how long can it deliver 2W, well, 2W at 6V is 333mA. You have 4.5Ah so it will last 13.5 hours. But that is theory. It will be a bit less, say 12 hours. I would never discharge below 5.5V; 5V at the very limit. At 5.9V the battery can aleady be called “empty”. Hope this answers your question.

On September 6, 2013 at 10:08pm
pavan wrote:

Hi Andre,
Thank you very much for your explanation, you clarified my doubts.

On September 21, 2013 at 4:35am
nimanabavi321 wrote:

excuse me, i have a question.

this is a summer of my state:
i charge my 12 volt car battery at 20 volt and 800 mA for 4 hours and continue with 15.5 volt and 200 mA and continue for 2 day.
after 2( 50 hours)  chargingggg the battery not starting car engine.
at now my battery open circuit voltage is 12.9 voltttttttttt.

NOW, i propose my question:
is my battery Destroy??????????????
Pls answer me.

many Thanksssssssssss.
Best Regards.

On October 8, 2013 at 5:49am
Andre Van den Wyngaert wrote:

although you only have put approx 13Ah (amp-hours) in the battery (0.8x4 + 0.2x50), it should be able to start the car, certainly when the open voltage is 12.9V. I guess that while you tried to start, the dashboard lights all went out, and then went on again when you stopped starting. This means the internal impedance of the battery has become too high. Maybe it has been discharged too deep. Or it is simply many years old. But I got the feeling you will indeed need to replace the battery…

On October 8, 2013 at 6:53am
Abdalla wrote:

I wanted to buy a rechargeable battery for our 80w solar panel for our holiday house. I have come across few of them but not sure which one is the best. one said 65aH/12v and other 100aH/12. my questions is what does these number stand for.
does it mean they supply 65a/100a per hour
is the 100aH better then 65aH
what does the 12v represent

On October 8, 2013 at 7:33am
Andre Van den Wyngaert wrote:

Hi Abdalla,
12V means that 12 volt is the nominal voltage of the battery. You should check if this is the correct value you need, depending on the charger you have.
The Ah value means “ampere-hours” and represents the battery capacity expressed as the product of current (amperes or also called amps) x time (hours). The higher the number, the more capacity. A 65Ah battery can deliver 65 amps during 1 hour; or 1 amp during 65 hours, or 6.5 amps during 10 hours, and so on. The 100Ah has more capacity, so it will take longer to completely charge it, but it will last longer while it delivers power. It is like a gas tank in your car. More litres/gallons take longer to fill but last longer. Disadvantage of 100Ah over 65Ah is price.

On October 8, 2013 at 9:59am
nimanabavi321 wrote:

very thankssssss for your Attention Mr Andre Van den Wyngaert dear.
my battery is good.

pls Mr Andre Van den Wyngaert add me to yahoo id.
my id at this site same yahoo.
i have a problem.
best regardssssss.

On November 2, 2013 at 6:53am
T Choudhury wrote:

Can I connect a Solar panel straight to the battery. I did and I am able to get more charging current .
I have 25W panel .
Is this a proper way to charge , if not Why is it so?
Will somebody help me on this

On November 5, 2013 at 4:23am
Pavan wrote:

Hi Mr.Choudhury,

you are not charging the battery in a proper way, why because read the above document carefully.

On November 9, 2013 at 4:06am
Okechukwu Kingsley wrote:

how do i determine the kw rating of a charger which i want to use to charge 12v 45AH battery in order to know the capacity of generator i need to power the charger

On November 14, 2013 at 9:54pm
Edgar wrote:

I bought a Enercell 12 V 5Ah Battery and UPG D1724 Sealed Lead Acid Battery Charger 6V 12V Switchable. I want to get an owner’s directions on how to use charger,how long do I have to keep it on the charger for it to be completely charger. Any response to this matter would be highly appreciated. Thank You

On November 20, 2013 at 6:50am
Gilbert wrote:

Can I use AC-DC regulated power supply to charge my 12V car lead acid battery?
Its voltage output 13.8V, 5amps?

On November 20, 2013 at 7:13am
Andre Van den Wyngaert wrote:

Hi Gilbert,
yes it will be perfect as long as the power supply is current limited. If it isn’t, your initial charge current will too high and damage the power supply. But most variable power supplies have current limiting. If you are not sure, you can connect a current meter (e.g. multimeter set for 10A full scale) in series with the battery and check if the current is not above 5A. If it is, disconnect immediately. Or you can short circuit the power supply with your multimeter (set to 10A full scale again) and check if the short circuit current is not above 5A. If the power supply is not short circuit protected, it can cause damage.
For the car battery, you can charge it at 14.5V as well. But once it is full (current has dropped to below 1Amp) you should lover the voltage to 13.8. You can keep it connected forever at 13.8V. It will stay full and ready for use.

On December 2, 2013 at 2:11am
Viking wrote:

There is a question here. I have connected lead acid battery of 12 V with Sunny Island inverter SI 5048. There is a sudden increase in the voltage per cell from 2.2 V up to 2.6 V when the SOC level is almost 100% ( fully charge). May I know is this good for the batteries? How does this happen ? Hope for your reply soon.

On December 2, 2013 at 3:21am
Andre Van den Wyngaert wrote:

Hi Viking,
http://files.sma.de/dl/5612/SI5048-TB-TEN110340.pdf - This datasheet says the 5048 has a complex charging algorithm (page 99 and up). But imho, 2.6V per cell is quite high. If it is a wet battery (car), it might be OK (car charge often goes up to 2.5V per cell) but for gel cells I’d say it is too high. The 5048 first performs a constant current charge with slowly increasing voltage, and then switches to constant voltage charge AT A LOWER VOLTAGE (according to the manual). If you say it suddenly switches to 2.6V per cell, something might be wrong. But then again, how “complex” is the charging algorithm…. Sorry, I cannot help you further on this.

On December 23, 2013 at 1:48pm
Richard Ferrari wrote:

My almost new 12 volt flooded cell battery was accidently knocked over during winter storage. Almost all of the battery acid has drained out of it. Can I add new battery acid to the battery, put it on my charger and save the battery, or is the battery ruined?

On December 23, 2013 at 3:24pm
Bob Kondner wrote:

If that battery was charge when it went over then acid was removed. You should be able to simply add new battery acid. It should act charged. This is how many batteries are shipped. They are charged, acid removed, shipped dry, and later acid added. You need to monitor the specific gravity of the acid when you do charge. If the battery was partially discharged then you will see the SG go too high. (Use other battery as reference. If So you need to remove some acid from the cells and add distilled water such that the specific gravity reach the correct value when fully charged, about 1.265

Bob K

On December 26, 2013 at 1:02am
George wrote:

How can I use a DC 110 volt motor (old one of a treadmill) to charge a lead acid batter of 200 Ah. The motor when working takes about 2.5 amps. When as a dynamo how much current can be drawn from it to charge the battery. And if the voltage is increased will the current drawing rate for charging come down

On December 30, 2013 at 4:11pm
Bruce McGillis wrote:

Drawing from a 120 power utility; how many amperes ( or expressed in watts) is being (used) drawn from the 120 volt power system to charge a battery at 3 ampere rate.
  Note: Assume a 100% charge.
Please reply to     bmcgillis@shaw.ca

On January 6, 2014 at 10:31am
Abhisar prince wrote:

A good site

On January 7, 2014 at 2:20am
mahmood gh wrote:

I use12V/7.2A lead acid battery for internet router . I use battery as secondary power source . The battery is contenusely concet to 13.8 V ( SMPS ) switching power supply . and from battery to router through voltage regular . 
Any problem or incorrect to stay battery contenusely connect to 13.8 volt ? Do i increase or decrease the charging voltage??

On January 7, 2014 at 2:21am
Andre Van den Wyngaert wrote:

Hi Bruce McGillis,
it is almost impossible to answer that question accurately with the numbers you gave. It depends on the battery type and voltage and the charger you use. Assuming it is a 12V car battery, and you have a charger that can deliver 10A secondary, with an overall efficiency of 80%, then the consumed power would be approx. 13.8Vx10A=138W secondary or 138/0.8=172W primary.

On January 7, 2014 at 2:37am
Andre Van den Wyngaert wrote:

Hi Mahmood gh,
I’d say you can keep a 12V lead acid battery (probably a gel cell if it is a 7.2Ah cell like you said) at 13.6…13.8V for its entire life. The cells I use have this value written on the body and they call it “standby use”.

On January 7, 2014 at 3:12am
Andre Van den Wyngaert wrote:

Hi George,
interesting question! If the motor draws 2.5A at normal load, I’d say it should not deliver more when used as generator. The copper wire and collector (I assume it has a collector since it is a DC motor) are designed for this current. So it can deliver 275W approx. (110Vx2.5A)
Now about voltage. I don’t know how your generator behaves when the load current is decreased below 2.5 amps. If the voltage raises above 160VDC, you cannot use the below solution.
But I think that you can use e.g. a Tracopower TEP 160WIR DC/DC converter: http://www.tracopower.com/fileadmin/medien/dokumente/pdf/datasheets/tep160wir.pdf or comparable. This one has an input voltage range of 43…160VDC, which should be good. The secondary DC voltage of this one is 15V, but you can adjust it down to -20%; so 13.8V is certainly possible, if you want to keep the battery connected all the time.  The power supply is 182W with heat sink mounted, so it will take care that he generator is never overloaded, since it will current limit the secondary. But you will have to take care that the DC/DC converter is good enough cooled, because it will have to work in ‘limiting’ condition almost all the time until your battery is full.
Like I already said, the only risk here could be that when the battery is full, the charge current drops to such a low value that the generator outputs a higher voltage than 160V which could damage the DC/DC converter. You should test that before connecting anything. A possible solution could be that you permanently connect a small light bulb to the generator, so you always keep the secondary voltage below 160V.
I hope this helped a little bit…

On January 10, 2014 at 12:23pm
FIYAZ wrote:

hi… I want to charge Sealed lead acid battery of 12V 7 AH with an adopter of 15V 1.2 Amp is my charger correct.? how long will it take to charge the battery fully. is there some indication that shows the battery is flly charged now. being sealed battery i can’t check specific gravity, i can only check voltage at 2 hour time strecthes and when it shows 13.2 volts. assuming each cell of 6 cell battery is 2.10 volts.
Weighting eagerly for your reply
best Regards
fiyaz abbas

On January 13, 2014 at 2:05am
Andre Van den Wyngaert wrote:

Hi Fiyaz,
you cannot connect the adapter directly to the battery, because you can damage the adapter. When the battery is empty, it will draw more than 1.2 amp, and the final charging voltage is too high as well. So you should reduce the voltage and the charge current a bit. It depends on the type of adapter how to do that. Is it a voltage regulated adapter or not? If it isn’t, you have more than 15V when there is no load (like 18V or more). If it is always 15V, it is regulated. In that case, you can reduce the voltage to 14.3V by adding a standard 3amp diode like 1N5401, and reduce the current by adding a 2.2ohm 5W resistor. Total cost 1 euro. So you connect the negative of the adapter to the negative of the battery directly, and the positive of the adapter through the diode and then through the resistor to the battery. So the resistor and the diode are in series. If you have no charge current, the diode is in the wrong direction and should be reversed.  Actually, the line on the diode should point to the battery. That’s all; it should work. Final voltage on a full battery will be 14.3V, so you should disconnect the battery then at the latest. But when the voltage is 13.8V, the current has already dropped to 200mA and not much charge is added anymore; the battery is then almost full. Since the charge current is decreasing while you charge, it is hard to tell how long it will take for a full charge. But I think 10 hours won’t be far wrong.
Best regards,

On January 16, 2014 at 11:25pm
schnitzelboy wrote:

Hi, I’m just a little confused about minimum temperature for charging a Lead Acid battery.  It says to never charge a frozen one, but what happens if you start charging warm and later it gets below freezing?  I believe it said it doesn’t freeze until -15 Celsius or because of the acid. 
I live in Calgary, Alberta and I am parking my car for the winter, and it is outside.  I have a 2A trickle charger connected to the battery inside my car.  It is smart enough to tell when it is full and switch to a charge maintenance mode.  Can I leave this thing on the battery all winter to keep it charged?  Keep in mind, it can get up to -40 Celsius with windchill, every once in a while.

On January 19, 2014 at 7:12am
George wrote:

I want to buy a deep cycle traction battery of 600 Ah 12 volts.

I like to make a solar panel for charging these batteries. What should be the capacity of
the solar panel in watts and the voltage out put and the current to charge these battery.

Alternatively if I use a wind mill what should be these numbers ( voltage out put, current capacity of the wind mill dynamo. )

appreciate your response. Kindly give any precautions I should take to have a better system that lasts long enough.

On January 22, 2014 at 7:06pm
Tom Calamaco wrote:

I bought a new 12V 7AH Sealed Lead Acid battery. Do i have to charge it when new before using it?

On January 22, 2014 at 9:12pm
George Mathew wrote:

Dear Andre Van den Wyngaert, Thank you very much for your reply about the DC motor dynamo. It was very informative for me Thanks again.

On January 23, 2014 at 1:52am
Andre Van den Wyngaert wrote:

Hi Tom Calamaco,
Lead batteries are never empty when sold. But it won’t be completely full either; it will be somewhere in between. I would charge it first to be sure you don’t discharge it to much.

On January 23, 2014 at 5:32pm
David wrote:

Dear Andre Van den Wyngaert, I’m designing a charger / psu for my boat. The batterybank is about 400Ah. As is the charger / psu can give about 4A @ 14,7V and about 26A @ 12V ( 16V @ 0A). It’ll not be a constant current charger but I can change how the power curve will be, but I’m not sure of how it should be.. I’m not sure how much power I’ll use when I’m in port. What voltage should I have on the charger / psu when I’m using power in port without making H2 gass when the battery is fully charged? I can make it up to 800W regardless of voltage, but I dont want to make it too complex, so I’m not making it with any PWM. I might make a cutoff @ 14,7V or a bitt less, but I hav not figured out how to make that work yet.

Should I lift the power curve a bit? (then i have to lift the no load voltage allso..) What should I do?

On January 24, 2014 at 6:50am
Andre Van den Wyngaert wrote:

Hi David,
like the explanation on top of this page says, you will need a topping charge voltage of approx 14.4V (or slightly higher if you wish). The current limiting of you supply will limit the current during the first stage of the charge (constant current) while the voltage raises slowly to 14.4V. The voltage then stays 14.4 (that’s the voltage setting of you charger) while the current will start decreasing. BUT you cannot leave the voltage at that level. Once you reach the 14.4V you can leave it there for max 48 hours, but then you must terminate the charge manually, or the charger must drop its output voltage to 13.8V. I have built such a circuit myself (for 5 parallelled 7Ah cells). Once the current drops below a certain limit (200mA in my case), the voltage goes down to 13.8V and stays there, so you can keep it connected forever.
Best regards,

On January 29, 2014 at 3:19am
KATY wrote:

can you please tell me, what is the maximum level of discharging the Battery in stand by mode

On January 29, 2014 at 5:11am
Andre Van den Wyngaert wrote:

Hi Katy,
that depends on some factors, but I’d say that it’s best to never discharge below 12V (if it’s a 12V battery). When you discharge further, you will see that the voltage decreases quite fast. Some say at 11.9V you can call it “empty”. You can go lower, but since the voltage drops so fast the delivered energy is negligible, and you will damage the battery.
If you stop discharging at 12V, I think it’s always safe.
Best regards, Andre

On January 30, 2014 at 12:40am
KATY wrote:

Thank u Andre and I am in need of one more information about temperature compensation. I got an information that there is a -0.05 V compensation in float voltage. is there any compensation in CC and CV too?. Can you please help me.

On January 30, 2014 at 2:10am
Andre Van den Wyngaert wrote:

Hello Katy,
I think the compensation in float voltage (CV in standby use) is -0.02V per cell for each 10°C the temperature raises.  So for a 12V battery it is -0.12V per 10°C. At 0°C it is 13.8V. At 10°C it is 13.68. And so on. Negative too: at -10°C it is 13.92V. 
I am not aware of any restriction of the CC charge current as function of the temperature. But that does not mean there isn’t any, of course… But when you are not really “on the edge” of allowable charge current for your battery, it won’t matter.
Best regards,

On January 31, 2014 at 1:55am
KATY wrote:

THank you andre. Sorry andre I have missed a term above. I am also in need to know the temperature compensation for the Gassing voltage. Can you please help me.

On January 31, 2014 at 2:43am
Andre Van den Wyngaert wrote:

Hi Katy,
I’m afraid I can’t help you on this one. On the internet, I found this table for lead acid 12V batteries::
-20°C: 17.82V gassing voltage
-10°C: 15.9V
0°C: 15.24V
10°C: 14.82V
20°C: 14.49V
30°C: 14.19V
40°C: 13.98V
50°C: 13.8V
Hope this helps you out…
Best regards,

On March 18, 2014 at 8:22am
T. Collins wrote:

Schnitzelboy -  About your cold weather concerns.  Keep the battery fully charged and you will have no issues with the battery freezing.  The Specific Gravity of the electrolyte of a fully charged battery will vary from battery manufacturer to manufacturer but should be somewhere around 1.3 kg / cubic dl. 

At this specific gravity the electrolyte will remain liquid at -60 degrees Celcius.  You can search the web for phase diagrams is you would like to double check my assertion.

Your trickle charger will offset the effect of self-discharge of the battery and the charging process adds energy (and heat) into the battery.

Bottom line:  No worries.

On March 19, 2014 at 5:50pm
binu a v wrote:

sir, i am an engineering student. i want to charge 12V 1.2Ah lead acid battery using a source which produce an output of 20V, and current in the range of 10mA, so can i charge the battery? if i can then provide me with required cicuitary please

On March 20, 2014 at 2:09am
Andre Van den Wyngaert wrote:

Hi binu a v:
charging with 20V 10mA is possible, but it will be slow. There are several ways to do it, and it will actually depend on some parameters you did not give. For example: should the current be limited, or can your source deliver “as much as possible” like a solar cell.
The below solution 1 has limiting. The others don’t.
1: use a simple series resistor. chances are small you will ever overcharge the battery with this small current. Value (20-13.8)/10mA = approx 560ohm 1/4 watt grin.  But just in case, you can put a zener diode over the battery to limit the voltage to 13.8V. A 14V zener will do, 0.5W, 10 cents. If you use a solar cell and there could be some discharging of the battery into the solar cell at night, you can add a small series diode 1N4148 betwen source and battery.
2: use a linear regulator to lower the voltage to 13.8V. You can find circuits on the internet with e.g. the LM317. It has an adjustable output, so you can set it to 13.8V (check datasheet, need 2 resistors: www.farnell.com/datasheets/1674527.pdf)
3: use a small 1W or so DC/DC converter like www.ti.com/product/lp2951. Is actually overkill, but in fact you could get some more charging current out of it. Input power is 20V 10mA = 0.2W. So you can get 0.2 / 13.8 = 14ma charging current out of it, if it had 100% efficiency. But it never has, so you probably won’t win a thing. It is a different situation if you sometimes have more power available and you want the most out of it (referring to the solar panel again). Then you could consider a DC/DC. They even exist in special versions for solar panels, where they search the most optimal working point to get the most power out of it. But probably not for low power like yours, so they would have higher cost and maybe more losses than benefits in your case.
If you need more information just ask, but please provide more details then.

On March 25, 2014 at 11:10pm
Jeff Bailey wrote:

What is the issue of using a 13.8V float voltage to charge 12V batteries?

I am needing to charge multiple independent batteries from a single power source (Solar panel). Using a 14.5V regulator and a 3A diode I can provide a maximum of 13.8 volts to each battery. Each battery is used for different loads - hence the multiple independent batteries. The batteries only get used on the occasional weekend so have a week or 3 to recharge.

I am sure this is better for the batteries than having them connected in parallel across a standard multi-stage solar regulator? Especially given that the batteries are different chemistries (mix of old and new SLA, an old car battery and an old truck battery)

On April 1, 2014 at 12:52pm
John wrote:

My automatic charger charges initially at 16V and I am concerned that this is too high.  I called the tech and he said that this is the design optimum. It has an AGM setting with initial charge at 12.5V which he said would not fully charge a conventional lead acid battery.

Please evaluate these comments. Thank you.

On April 1, 2014 at 1:03pm
John wrote:

Sorry: AGM voltage corrected.

My automatic charger charges initially at 16V and I am concerned that this is too high.  I called the tech and he said that this is the design optimum. It has an AGM setting with initial charge at 15.5V which he said would not fully charge a conventional lead acid battery.

Please evaluate these comments. Thank you.

On April 8, 2014 at 9:48am
wynn wrote:

Hello writer, you have a great and helpful article. I am hoping that you could help me with my problem.
I am working in a plant. Our system requires 24VDC Back-up Supply. In the battery room, the setup is like this: 4 12VDC batteries are there. They are divided in two groups. Each group is composed of batteries connected in series to form a 24VDC Supply. The two groups are connected in parallel to the charger. The Charger Voltage is 29.4VDC and Charger Current is 40.1A. The charger is set to float charging. These are the problem: 1. Group no. 2 is overheating. 2. Group no. 2 has seen gassing in the cell cap. Is my system still normal? If not, can i ask you some recommendations on what to do?

On April 15, 2014 at 8:08pm
Jagat Modi wrote:

Can any body share the probability of lead acid automotive battery being exploded durting cracking of an engine ? And also the same battery being used for DG starting with permanent float cum boost charger connected ?
And what are the SOP for lead acid batteries used for such applications ?

On April 16, 2014 at 7:15am
Azerty wrote:

My 12V 18 Ah lead acid battery is fine after charging, there is no trapped gas. But if I let the battery sit for 24 hours (nothing connected to the terminals) and I tilt the battery slightly, pea sized gas bubbles appear from between the plates and bubble to the top in more than one cell. As if gas develops over time which is trapped between the plates and can not escape to the top apart from at the sides (by tilting 10-20 degrees).
New gas appears every day.
Is this normal, what does this say about the battery, is it ok (to use) ?

On April 19, 2014 at 3:05pm
Kawika wrote:

Is there a formula of the amount of amps for proper charging of AGM batteries? I am taking a 600 AH string off line and putting a 150 AH string in place for a temp string but I don’t want the rectifiers to cook the batteries. I can adjust voltage if need be but want to understand if I need to adjust the amps. thanks

On April 25, 2014 at 3:48am
karthik wrote:

Dear sir,
    I have 12v,7.5amps Lead acid battery.so i need to charge this battery by 12v dc,3.5amps SMPS.If it is possible or not

On April 28, 2014 at 1:02am
Andre Van den Wyngaert wrote:

Hi Karthik,
you need 13.8V float voltage and preferrably 14.5V topping charge voltage to charge a 12V cell. You cannot do it with a 12V SMPS. Maybe there is a possibility to tune the SMPS to 13.8V?

On April 28, 2014 at 1:07am
Andre Van den Wyngaert wrote:

Hi Wynn,
you say the charger is set to float charging. Yet the voltage is 29.4V DC which is way too high for float charging lead acid batteries, in my opinion. You need approx 27.6V for float charging. If your voltage stays 29.4V all the time, you stay in topping charge as described on page 1 of this article.

On May 13, 2014 at 8:05pm
Jasmine Martinson wrote:

Hello, I have an inverter and 12 x 6volts batteries along with a generator for changing purposes. Just bought 12 new batteries I am in a 3rd world country and they fill the acid in the batteries when they get here. Wondering if these batteries should be floated before used. Also how long should they be charged and on what level of charge I am in Haiti and it’s above 90 F almost all the time. Thank you for your kind reply.

On May 14, 2014 at 6:16am
Bob Kondner wrote:

  It is normal to ship the batteries dry and fill them with acid as they are sold.

When manufactured the plates are build using PbO2 which is the charged condition. When the acid is added they act as fully charged..

It will take a few cycles to reach full capacity and the pressing of PbO2 into the plates does not seem (my limited observation) to form the best contact. After 2 or 3 cycles you should see full capacity or better.

Bob K.

On May 20, 2014 at 8:16am
David Franer wrote:

How can I read the anxwers to the questions posed on the page?

On May 21, 2014 at 1:21am
Andre Van den Wyngaert wrote:

Hi David,
this is actually a “comments” page. But since some people started to ask questions and some people started answering them, you will find answers to some questions between the comments. At least, they are in chronological order, so if someone gave an answer you will find it somewhere below the question…
Good luck!

On May 22, 2014 at 4:29pm
George wrote:

I have an unusual application where I need short bursts of high power but much much lower average power.  The idea is to use a battery bank to provide the peak power with a much lower power charger and prime power source (ac mains or motor-generator) to supply the average power, i.e., using the batteries as a buffer. 

Here is a nominal scenario employing 50 88 Ah 12V automotive starter batteries.  The worst case (<5% of cycles) the power rapidly ramps over a few seconds peaking at 200 kW and then slowly tapering down to near zero over the next 45 seconds or so.  The peak current required is thus around 350A and the total energy required for a cycle is less than 1.75 kWh. Then the system has at least 10 minutes to rest/recharge.  More nominal cycles are at 2/3 these levels and commonly less.  (Operation is over the daytime only and there will be extended periods (days) where saturation charging can be applied using best practices.  Operating temperatures will rarely exceed 35 C and storage will typically be at 20 C or less.)  The charger power is under 15 kW so the charging rate is C/3 or less.  A key requirement is durability – on the order of 10,000 cycles – which further drives using a large number of batteries to reduce the stress (DOD and peak current). 

An 88 Ah 12V battery holds about 1 kWh so 50 hold nearly 50 kWh.  So the worst case depth of discharge from one cycle is about 1.75/50 or only about 3.5% and more typically under 2.5%, i.e., essentially micro-cycling.  So many batteries are employed to provide the peak power and for durability, not for the energy capacity. Calendar lifetime is also a strong consideration and leads me to my real question.  In Batteries for a Portable World, Revision 3, page 217, there is mention that stationary batteries employ a lower acid concentration (SG ~1.225) to reduce corrosion and prolong calendar life.  Would it make sense to dilute the electrolyte in the automotive starter batteries to around this level to improve calendar life?  I understand this would reduce the open cell voltage a bit requiring somewhat more current (or adding a couple more batteries) but could this move the calendar life out well beyond 5 years?  I see references for up to 10 year service life for stationary batteries and I assume operating with lower SG to reduce corrosion is a big driver.

Ideally I would like to be using lithium-phosphate to provide the power/durability at much lower weights but capital costs and BMS complexity are important considerations for a prototype demonstration system.  [An even better solution is using ultracapacitors but I will not go into that.]  Hopefully when these initial batteries become marginal in 5 – 10 years the lithium (or ultracapacitor) option will be more palatable but this is a potential bridging strategy until that time.

On May 22, 2014 at 5:45pm
Bob Kondner wrote:

  I have been looking at something similar here but at 2KW. I would worry that 200KW from 50 pieces of 88AHr 12V batteries is probably not going to work. t 350A load is going to drop your battery voltage terribly. And dropping the voltage probably means you will need MORE current.

I have a 12V 350AHr battery (2 pieces of Rolls 460) and getting 200A at 10V delivered to my load terminals is difficult. Batteries, wires safety devices, the drops all add up.

I would be very curious what you get for battery voltage during a 45 second test at 350A.

Bob K.

On May 23, 2014 at 8:21am
George M wrote:


I have not constructed the system yet so all I can do is an analysis.  These would be starter batteries with CCA values >900 A.  That says they can produce 900 A (new) for 30 seconds at 0 F without falling below 7.2 V (1.2 V per cell).  The operating temperature in this application is rarely under 50 F and more typically 70 F or higher.  This is more in the Hot Cranking Amperage temperature range which yields considerably higher current ratings, let’s assume 1400 A HCA.  If the open cell voltage is >2.2 V the string voltage is > (50*6*2.2) = 660 V.  1400 A HCA should guarantee that the voltage drop is less than 350/1400 * (2.2 - 1.2)  = 0.25 V/cell.  This would drop the string voltage to no less than 50*6*1.95 = 585 V.  350 A at this voltage would be 205 kW.  (This does ignore cabling drops so maybe a little higher current.)  Note that the peak power only lasts a few seconds and then tapers off to near zero by the end of 45 seconds.  This means the battery current will also be dropping to near zero (and the loaded string voltage rising) over a cycle.  So 350 A is the peak current, not a constant current over the cycle.  And again I need to reiterate this is the worst case condition that applies to less than 5% of cycles.  More typically the power levels are 2/3rd this level or below.  Automotive starter batteries are employed for their power density.  Deep cycle batteries would not be appropriate for this application. 

There is an existence proof for batteries used in a similar application that are currently achieving 5+ years of service life.  This means the lifetime issues are getting into the calendar life limits of the batteries.  My question is, can I increase the calendar lifetime of batteries in the application by intentionally diluting the electrolyte towards the value used in stationary batteries?

On May 23, 2014 at 9:37am
Bob Kondner wrote:


Yes, a starting battery would be more appropriate than my deep cycle.

Can you test a single 12V battery and see what it does? I would be very curious as to the voltage drop.

I just ordered a small quantity of LiFePO4 cells (18650 sized, about 1AHr) with 35A continuous rating. (About $3 a cell) I want to measure the pulse characteristics. I do wonder if nanoparticle Li (like what A123 was producing) would be the cheaper route. You could get 120A for 10 sec out of those. For 200KW you are talking about 550 cells.

Bob K.

On May 23, 2014 at 12:31pm
George M wrote:


I am still about a 9 months from starting prototype construction and purchasing the batteries will be one of the last component sets acquired for just this calendar lifetime issue.  The CCA test is very definitive and my analysis above should be conservative.

What I use for the power buffer is not fundamental to what I am trying to demonstrate in this prototype.  I would like to use LiPo similar to those produced by A123 but the cost and BMS complexity are unacceptable at this time.  Your cost is better than I have heard for such high-C rate cells.  Can you share your vendor information.


On May 23, 2014 at 1:30pm
Bob Kondner wrote:


hugebattery.com They quotes a IFR18650 at $3 for quantity 20. I still have to receive a datasheet so I am still totally in the dark on these. For me I just need 2KW for short (IE Motor starting periods) bursts. Deep cycle batteries after that.

I am bob at kondner dot com and Skype: rkondner

Give me a shout and we can take it off line.


On June 2, 2014 at 4:56am
George Moore wrote:

I posed a question in my post of 6/22 above that has not yet been addressed by anyone.  I got into a side discussion with Bob Kondner but the fundamental question was never addressed. “Would it make sense to dilute the electrolyte in the automotive starter batteries to around this level [that of stationary batteries] to improve calendar life?  I understand this would reduce the open cell voltage a bit requiring somewhat more current (or adding a couple more batteries) but could this move the calendar life out well beyond 5 years?”  Further details of the application can be seen in the referenced post.

Any comments to these questions would be much appreciated.

George M

On June 24, 2014 at 6:52pm
George M wrote:

One Last Time:

I posed a question in a post of 6/22 above that has not yet been addressed by anyone,  “Would it make sense to dilute the electrolyte in the automotive starter batteries to around this level [that of stationary batteries] to improve calendar life?  There is reference to some stationary batteries having up to 20 year lifetime attributed to reducing the specific gravity (acidity) to reduce corrosion.  I understand this would reduce the open cell voltage a bit requiring somewhat more current (or adding a couple more batteries) but could this move the calendar life out well beyond 5 years?”  Further details of the application can be seen in the referenced post.

Any comments to these questions would be much appreciated.

George M

On July 9, 2014 at 1:16am
Mark Hull wrote:

To George M:

I don’t track BU posts much, but yours caught my eye. I hope this doesn’t come too late.

I am/was an aerospace electrician for over 30 years. I am not an engineer, but having worked in the battery shop for several years I beleive I can give you some usefull information.

Reducing the S.G. of the electrolyte would theoretically increase calender life. However you would also be decreasing capacity. When manufacturers of starter batteries started offering 3 year no pro-rated replacement, reducing the S.G. of their batteries to reduce grid corrosion was one of the things they did in order to offer that warranty..

The 20 year batteries you’re referring to are generally constructed with solid lead plates aka Plante type cells. Depending on who the manufacturer is sometimes it’s only the positive plate. That said, and after reviewing your original post, IMHO using flooded batteries is not your best option. AGM batteries are. This is due to their very low internal resistance. They are able to supply very high rates of current while generating very little heat. You didn’t specify if all your batteries are in parallel connection, but I am assuming from your original post that they are. Also what you described in your original post sounds very much like the requirements needed by those who build those mega watt audio competition cars and vans. Originally, they used very large capacitors to augment the quick response required by their MOSFET amplifers driving large subwoofers. For the most part they are all now using AGM batteries simply because AGM can supply the extremely quick reaction time needed by the amps and are able to supply it for much longer times than what the capacitors are capable of. AGM also offers very quick recharge times of C/5 or greater. You also stated that you were looking for a 10,000 cycle lifetime. I don’t know of any manufacturer that has tested their batteries under the conditions you’re wanting including the LiFePO4 ones. That said, I still beleive that AGM offers the best option concerning lead-acid. Heat is the enemy. Whether from external ambient or from charge/discharge cycles. Since your external conditions seem well controlled, your left with the latter. Again, due to the ultra low resistance AGM is the only way to go. Odyssey battery and Concorde/Lifeline are the 2 manufacturers that come to mind. I also wouldn’t count out Fullriver Battery either. They are Chinese in orgin, but they’ve had overall good reviews.

I also don’t beleive you need anywhere near 50 batteries for a max discharge of 350 amps over 45 seconds. I think you could get by with 10 or less group 31 size batteries.

The other extremely important consideration in longevity is charging. Since no 2 batteries charge at identical levels, they should all be charged individually. This is borne out in the golf cart world where 6 to 8 batteries are connected in series and charged by either a 36 or 48 volt charger. This set-up always leads to premature failure since some of the batteries in the string charge before the others do leading to an overcharge in some and under in others. In a parallel string you still have the same problem. Individual charging is the only solution for maximum lifespan.

So what would I do in your situation in light of no hard data to draw from. I would start with 8 Group 31 AGM batteries and 2 each four bank marine chargers. Procharge or NOCO are the two best multibank chargers out there for the money. Charles Industries chargers also offer a much more sophisticated charger that allows you to program the charge parameters yourself (but at a premium price too). Then I would start tracking the performance data and add banks on an “as required” basis. I think you’re going to be surprised at how well the smaller group will perform. I’m going to check the “notify me” on this. I would be interested on how your project goes….


On July 9, 2014 at 10:05pm
Mark Hull wrote:

To George M,

I had some more time to reflrct on this. Fullriver makes a Deep cycle AGM battery in the BCI standard 8D. These 175 Lb behemoth’s are rated at 1830 cranking amps ar 32 degrees F. This is a standard 30 second test before it drops below 7.2 volts. I would think that 1 or 2 of these at the most should siffice your requirements. This would dramatically reduce the number of connection points improving overall efficiency. Just my 2c.

On July 10, 2014 at 5:55am
Bob Kondner wrote:

If you look at George’s requirements you see a short period (10s of seconds or so) at 200KW.

To 1830 Amp at 7.2V is only 13KW. he would need about 13 of these “Behemoth Batteries”.
Bob K.

On July 10, 2014 at 6:23pm
Mark Hull wrote:

Hi Bob,

Point taken. Probably shouldn’t be posting at 1:20 AM. I was zeroing in on the 350 peak amp. But something still doesn’t add up. How can he have a 200,000 watt peak and a 350 Amp peak in the same cycle? If I still remember Ohm’s law correctly;

350A x 12.6V = 4,410 watts (ignoring voltage drop for the moment)
200,000 ÷ 12.6 = 15,873A (not the 350 as stated).

So how can he have a 200kW (200,000 watts) and a 350 A peak in the same 45 second cycle?

Also, he states that an 88 AH battery has about 1kW. It would appear that he’s just multiplying 12V x 88A = 1,056. He’s not taking Peukert’s law into account. Starter batteries are all rated at a 20 hour rate, not a 1 hour rate.

Like I said, I’m not an engineer, nor do I profess to be an expert by any means. I reviewed his post several times and the math is still not adding up to me. Am I wrong? It’s got me wondering now. (Almost wish I hadn’t jumped in now. It always gets me in trouble).

Kindest Regards,

On July 10, 2014 at 7:04pm
Mark Hull wrote:

Hey Bob,

I just went over his May 23rd post reply to you. In his original post I can’t determine if he’s designing his battery bank in series or parallel. On his May 23rd post it would appear it’s series??? Is he needing high voltage 585? 660? at 350A. Or is he needing 350A at 12.6V?  350A for 45 seconds at 12.6V isn’t much of a problem. If he really is needing the 200kW, WOW! I don’t think the Tesla needs that!!!

AGM’s are still the only way to go though IMHO.



On July 11, 2014 at 6:35am
Bob Kondner wrote:


At 200KW you want to work with as high a voltage as is reasonable, and the and the load is very importance naturally.

600V is probably an upper limit, that is 330 Amps for 200KW. That would be 50 pieces of 12V batteries in series.

Their is a problem drawing high currents from a 12V battery such that the voltages drops below 8V, the problem is about 50% of the power is being dumped into the battery as heat. Draw 1000A from a starting battery and see how long before it starts to generate steam!

On July 11, 2014 at 12:09pm
Mark Hull wrote:

Hi Bob,

Agreed. Ohm’s law. Increase voltage, decrease amps. But you still don’t want to use flooded batteries in this application for the very reasons you state. I wish the OP would clearly state what their actual voltage and amp draw requirements are. Because 200 kW does not equal 350 amps at 12.6 volts. That violates Ohm’s law. I looked up the Tesla battery back. Taken from Wikipedia. The referances used are sound:

“Tesla Motors refers to the Roadster’s battery pack as the Energy Storage System or ESS. The ESS contains 6,831 lithium ion cells arranged into 11 “sheets” connected in series; each sheet contains 9 “bricks” connected in series; each “brick” contains 69 cells connected in parallel (11S 9S 69P). The cells are of the 18650 form-factor commonly found in laptop batteries. Sources disagree on the exact type of Li-Ion cells—GreenCar says lithium cobalt oxide (LiCo),[112] while researchers at DTU/INESC Porto state lithium manganese oxide (LMO).[113] LiCo has higher reaction energy during thermal runaway than LMO.[114]

The pack is designed to prevent catastrophic cell failures from propagating to adjacent cells (thermal runaway), even when the cooling system is off.[115] Coolant is pumped continuously through the ESS both when the car is running and when the car is turned off if the pack retains more than a 90% charge. The coolant pump draws 146 watts.[45][116][117][118]

A full recharge of the battery system requires 3½ hours using the High Power Connector which supplies 70 amp, 240 volt electricity; in practice, recharge cycles usually start from a partially charged state and require less time. A fully charged ESS stores approximately 53 kWh of electrical energy at a nominal 375 volts and weighs 992 lb (450 kg).[119][120]”

I have much personal experience starting stationary diesel engines in the cold. Most were using 24 volt ststems and 4 8D batteries in series/parallel configuration. Their starters pull well over 800 amps. I’ve had to crank these over 30 seconds and I had a digital volt meter to monitor the batteries. Voltage never dropped below 20 to 21 volts until after about 45 seconds. Oh well, seems he’s not monitoring the discussion board anyway. Have a great weekend! I’m outta here….......


On July 27, 2014 at 11:36am
tonykid wrote:

Question. MY solar battery can’t reach even 12.8V in what ever charger I charge. pls what should I do

On July 27, 2014 at 5:26pm
Bob Kondner wrote:

Well, you have a problem. Hookup a cheap automotive charger but not for long. You should see that bring up the battery voltage. Do not leave such a cheap charger on your battery for long, cheap auto chargers will damage batteries if left connect for a long time.  You did not give a lot of info about your system but 12.8 is pretty low for a peak charging voltage.


On July 28, 2014 at 2:07am
tonykid wrote:

Sir is the battery ok,because I used many different type of charges

On July 28, 2014 at 9:24am
Bob wrote:

You have not given me enough information to confirm that you battery is good or bad. You did not state the capacity and type of batter nor did you supply information about charging time and current. Gather that information and ask again.


On July 29, 2014 at 1:26am
Mark Hull wrote:

+1 Bob.

Need the following:

1. Brand of battery (preferrable to look up specs
2. AH rating (20 Hr rate)
3. Age of battery in service (very important)
4.Type of battery (flooded, AGM, or Gel) (also very important)
5. If flooded, what is specific gravity of electrolyte each cell?
6. List chargers used and what settings you used.


On August 4, 2014 at 11:53pm
ashwanth wrote:

List chargers used and what settings you used

On August 16, 2014 at 12:22am

In a LEAD-ANTIMONY Battery Factory ,
1) where plates are charged in SERIES CONNECTED VATS at FORMATION SECTION through a CONSTANT Voltage RECTIFIER , what is the detail formula for determining the optimum Current and Optimum charging time ?
2) What are parameters ( CCA , OCV , SG of H2SO4 , etc. ) and what range of value are confirmatory to a low knowledge Battery workers that each of the BATTERY , he is sending to Customer are well PASSED ?
3) Which of the following option is better in terms of quality and why—
a) Battery produced from Charged plate ( as stated above ) followed by H2S04 Acid filling followed by Bo0st Charge with Battery Charger .
b) Battery produced from NO Charge plates followed by H2SO4 filling followed by Charge by Battery Charger .
4) What type of Charger will be most appropriate to CHARGE our battery mentioned at 3( a) or 3( b) ? Is it a constant voltage Charger ?
5)What is the formula for determining the specification ( VOLTAGE & AMPS ) of a above noted ( point-4 )charger with Number of Battery are in series connection ?
6) If we made a graph with the voltage and amp. shown at the meter connected with the above mentioned constant voltage charger with time of charging ( MINUTES ) , what will be the shape of this graph ? At what point of the graph , operator will understand all the series connected Batteries are optimum charged .

On August 16, 2014 at 12:26am

In a LEAD-ANTIMONY Battery manufacturing Factory ,
1) where plates are charged in SERIES CONNECTED VATS at FORMATION SECTION through a CONSTANT Voltage RECTIFIER , what is the detail formula for determining the optimum Current and Optimum charging time ?
2) What are parameters ( CCA , OCV , SG of H2SO4 , etc. ) and what range of value are confirmatory to a low knowledge Battery workers that each of the BATTERY , he is sending to Customer are well PASSED ?
3) Which of the following option is better in terms of quality and why—
a) Battery produced from Charged plate ( as stated above ) followed by H2S04 Acid filling followed by Bo0st Charge with Battery Charger .
b) Battery produced from NO Charge plates followed by H2SO4 filling followed by Charge by Battery Charger .
4) What type of Charger will be most appropriate to CHARGE our battery mentioned at 3( a) or 3( b) ? Is it a constant voltage Charger ?
5)What is the formula for determining the specification ( VOLTAGE & AMPS ) of a above noted ( point-4 )charger with Number of Battery are in series connection ?
6) If we made a graph with the voltage and amp. shown at the meter connected with the above mentioned constant voltage charger with time of charging ( MINUTES ) , what will be the shape of this graph ? At what point of the graph , operator will understand all the series connected Batteries are optimum charged .

On August 16, 2014 at 8:27am
Bob Kondner wrote:

You asked so many complex questions it is difficult to help but let me try.
1. If you have pre-charged plates then the concentration of H2SO4 will be fairly high. I suggest you find a manufacturer of a similar battery type and read their application notes.

2. A NO CHARGED plate will require a lower level of H2SO4 as acid will be formed as PbSO4 converts to H2SO4 during charging. Ensuring a quality battery is being shipped is difficult. My suggestion is find a discharge profile for a “Good” battery and verify each production battery matches that profile. But it takes time to construct and verify a profile. The time and equipment required to verify each battery might be too costly. Sample the batteries coming out of production if required be you can count on some percentage of bad batteriests being shipped to the customers.

3 I think construction from charged plates I I understand PbO2 is pressed into plates, I never heard of PbSO4 being used in plate construction.

4. Asking what is the “Best Charger” is a little silly, there are many different aspects to charging a battery, the best depends on the application. In General you want a multi staged current limited constant voltage where the applied voltage varies with the various charging phases.

5. There is no fixed formula. The literature from books and manufacturers is filled with all types graphs and charts.

6. Look at the top of this web page! Look at the literature. Make your graph and make certain it matches!

Bob K.

On August 30, 2014 at 4:39am
Jeff Deutsch wrote:

I have an old Sears 10A.unregulated, manual or auto shutoff battery charger. The auto shutoff circuit is three transistors with an adjustment pot, driving an SCR. Because of the voltage drop in the SCR it always charged at a couple of amps higher in manual mode, with the SCR bypassed. It was not working in auto or manual and I checked transistors and SCR and when all checked out I put it all back together and it worked but not quite right in auto. I’ll probably never know what was wrong. In auto mode it used to shut off cleanly but now it will drop to a couple of amps and not shut off but if I switch to manual for a minute and back auto it shuts off but then comes back on after a minute. . I’m pretty sure I am putting a higher top charge in manual that quickly bleeds off. The fact that it can shut off tells me the SCR is OK but the shut off pot probably needs to be readjusted. For a maintenance free car battery, do I set cut off while connected until charger shuts off? Is 13.5V correct or another voltage?  Can it even be set while connected or do I have to tweak the pot until I get 12.6V. while disconnected after top charge has bled off? Thanks.

On September 6, 2014 at 1:58am
kapil G. wrote:

I am using 2 sealed lead acid batteries of 12V, 3.6 Amp Hr. in series to get 24 V , I want to use two stage charging algorithm CC-CV, I want to know what should be ideal current for cc modeand ideal voltage range in CC mode and when to shift from CC mode to CV mode in terms of state of charge or in terms of battery charging voltage.

On September 23, 2014 at 3:10am
Andre Van den Wyngaert wrote:

Hi kapil G. ,
It depends on the manufacturer of the cells - maybe you can check the website. But 3.6Ahr you can typically charge with 800…1000mA maximum; I would take 500mA as a max to be on the safe side.
So for 2 cells in series, current is still 500mA. Max voltage is approx 29.5V. So you keep CC 500mA until the voltage reaches 29.5V. Then you keep the voltage constant at 29.5V until the current drops to approx 100mA. Battery is full at that point. Then you lower the voltage to 27.6V and keep it there forever if you want.

On September 23, 2014 at 7:27am
kapil G. wrote:

Thank you ’ Andre Van den Wyngaert ’  , your suggestion will help me. I will work over it . If any problem persist i will post here.

also, Thanks for Battery University!

On October 18, 2014 at 10:29am
alan daykin wrote:

Some time ago I read an article on rejuvenating deep discharge battery’s by over voltage charging for a short spell .can anyone help as it was on my old pc.

On November 1, 2014 at 2:09am
OH wrote:

I’m new here.
I wish we could share knowledge in this amazing batteries website!
Thank you all!

On November 4, 2014 at 4:06am
S T wrote:

nicely done, very informative.
thanks a lot.

On November 20, 2014 at 3:08pm
JR wrote:

I have an off- grid cabin with the following electrical setup:  Two “banks” of batteries connected with a 1-2-ALL-OFF marine type manual switch, a 45A Progressive Dynamics RV battery charger/power supply, and a 1500W inverter.  The charge comes from a gas powered generator.  The primary battery is a pair of 6V golf cart GC2’s in series and the secondary is a 12V deep cycle marine.  When set to “ALL” both banks are connected to each other. When the generator is running, whichever bank is selected on the switch is connected to the charger, and also the house load.

My question is,  What is the best method of charging “bang for buck” wise as far as time running the generator?  My tendency has been to use each bank separately until both reach discharge (warning sounds on inverter) then set the switch to “ALL” and charge both banks in parallel for the bulk charging portion.  Then after the total voltage comes up (all batteries in parallel) after a few hours of running the generator, charge each individually (set to 1 or 2, not ALL) for the remainder of the charge, alternating between each so they can rest.  Is this correct, or should I be bringing them both to full float charge completely separately?  The only reason I don’t is it’s a lot of generator run time at a very low load.  With both banks in parallel do the pair of 6Vs and the 12V balance out to the reading I see on the inverter’s display, or am I really overcharging the smaller capacity battery?  I would appreciate suggestions - OR is this a case for a battery isolator?  If so I’m not sure how that wiring diagram would look.



On December 3, 2014 at 9:20am
joshi wrote:

Can any one tell me how long can a brand new lead acid battery without electrolyte be kept before subjecting to initial charging (48 V 300 ah).

On December 3, 2014 at 4:19pm
Elaine wrote:

I have a Cyclops Thor 15 Million Candle Power Rechargeable Spotlight that I bought 3 years ago but that I’ve never used.  When I turned it on, I got nothing.  How long would I need to keep the unit plugged in for it to recharge?  Is it possible the battery can never be recharged?

On December 5, 2014 at 9:22pm
joshi wrote:

Thanx Mr John Bradshaw for the reply.

On January 9, 2015 at 11:17am
Joan wrote:

I would invite everyone interested in knowledge to check out the ideas of Tesla and Bedini.
There are lot of places to go but one could start at Tesdlachargers.com.  Ignore the stupid glitzy cheap advertising (it will turn you off), and listen to what they are saying and watch the videos.  I have bought one of their small chargers, and can fully attest that you batteries will return to full life and provide more power than they have for years.
14.7 volts on a 12 V system does not seem to be enough to fully recharge them, so they slowly die.  With these chargers, there is no overheating problems, no off-gassing (except a the very end just as it is fully charged).  Do Not Throw out a seemingly dead battery until you have checked this out.

On January 11, 2015 at 8:40am
Dave wrote:

Just a general question. I understand that the voltage range for charging a 12v battery has to be above 2.19V per cell and less than 2.5V per cell, but I was wondering if anyone could give me the min aand max current range for charging. I have seen different answers, some stating C/10 so if I had a 20 AH capacity I would be full charged in 10 hours while charging at 2 A. I`m just wanting to know what the save charging current range would be, min and max values.



On January 23, 2015 at 11:38pm
Samir Das wrote:

In wet charging process around the battery terminal, there form some greenish substances,
Is this Iron (II) sulfate or anything else? From where this is came from? 1) Nut bolt 2) Cable Lux or from anywhere else??
Is there any possibility of forming any other substances?
How can we solve the problem?

On February 12, 2015 at 6:00pm
David Devine wrote:

Dear Sir,

I am using 6 volt 232 ah batteries for a battery bank. For now I have two to give me 12 volts to the 3500 watt inverter. This is used for emergency power in the event of a power failure. I would like to know what you would suggest for a charger maintainer to recharge and care for the batteries.

On February 27, 2015 at 7:49am
Ludwig Lindermann wrote:

Hello everyone!!

I need help with my doubts, can I charge a lead-acid battery with a solar panel without charge controller? how long the battery supports overload after being charged? and how long nickel-cadmium battery suports overload after being charged?


On March 11, 2015 at 9:33pm
Morad Massalha wrote:

Question about battery recondition with EPSOM:
1. I take the battery charge acid, clean it several time with distilled water.
2. Fill with DI and EPSOM, about two oz for cell.
3. Do charge with non-smart charger, the current is very high more than 20A, so I try to reduce current by adding resistor or lamp and current became low about 5A, but the voltage is low so no charge because the voltage on battery drops to 10V maximum.

My theory to this :
1. Because I drain the chemical from battery I diry space between cells plates then I have shorts and battery resistance became very low and current will be high.
2. EPSOM too much and I need to seperate it to MG+ Sulf and this take time and my charging method not possible to do this.
3. When I charge at least three cells no bubbles and voltage decreased after 5 min to 6-7V, looks hard shortage that decrease voltage.

What do you think about my battery recondition process?

On April 4, 2015 at 6:22am
zoha wrote:

sir i have a lead battery .one of the cell creates noise ...and also smoke(steam) come off .......kindly tell me how i got solution…

On April 9, 2015 at 10:53pm
Roni wrote:

Sir, I have question. I a UPS. I used it on my Desktop Computer. But now it’s battery is died So, I want to use there a more powerful battery for long backup. I want to use 100Ah battery (I will use extra charging syster if UPS charging system not working)
So, My question. Can I use Lead Asid battery on my UPS?

On April 15, 2015 at 11:15am
yasir wrote:

Sir,I have a battery charger of 12v 20amp for charging 12v 175 amp battery,Input required by charger is 220v AC and it gives output of 12V DC 20Amp
Can you please tell how much Watts of electricy will charger take to give 12V 20 amp output.

Input requiredby charger:220V AC
Output:12V DC


On April 15, 2015 at 9:12pm
Roni wrote:

Thank for your question.
You will be get 190-210 watts.
(P=V*I*Cos® or P=I*I*R)

But, You sad Your charger is 12V 20Amp and bettery is 180Amp. But how is possible to charge by 12 V 20 amp charger. You have to update your charget rating. You need 12-0-12, 8 to 10 Amp transformer.

If you want to get more power (watt) from output so, I can get it easily. First you have to update your machine. If you use this bettery on IPS so, you be get minimum 200watt to more. Just find out of your charger, how much it’s output VA (VA 80%=Watt).

On April 15, 2015 at 9:17pm
Roni wrote:

Thanks* (Charger rating)* (so you will be get it easily, First you have to update charging machine FET)*

On April 17, 2015 at 12:51am
Andre Van den Wyngaert wrote:

to Yasir:
A 12V 20Amp Lead acid charger will deliver 14V or so at maximum. So, theoretically, it takes 14 x 20 = 280 Watts. But there will be some losses in the charger, so it could take even a bit over 300W.
Best regards,

On April 17, 2015 at 12:58am
Andre Van den Wyngaert wrote:

to Roni:
depends on which UPS you use. But if there is a lead acid battery inside now, you can replace it with higher capacity external lead acid battery with the same voltage. Charging will take longer, but I see not other problems.
If there are now 2 or 3 batteries inside and they are placed in series, you need to do the same for the external battery to get the same voltage!

On April 18, 2015 at 8:28am
bashar wrote:

i want to know when
a lead acid battery fully charged then we find 2.1volt in per cell but my ask why 2.1 volt ? what is the main calculation and when discharge a battery then 1.75volt in per cell? please tell me in a details.

On April 18, 2015 at 8:36pm
Roni wrote:

Andre Van den Wyngaert

Now I using a mini UPS. It’s 600VA. Actually I using it on my desktop conputer. But now it’s bettery is down, I saw the UPS bettery, it’s JYC 7.5Amp Battery not Led acid bettery, but now I want to use there a more powerful Lead acid bettery (minimum 100Amp) bettery. So, can I replace there a lead acid bettery? (I shall use a external charger for charge bettery) So, I needs to know that If, I use a external Lead Acid Bettery on UPS, So will be any problem on my UPS?

Best regards,

On April 19, 2015 at 11:21pm
Aatif Anwar wrote:

sir i have design lead acid intelligent charger which works properly. with thats charger now i am designing a battery protection circuit for same lead acid battery charging circuit, which cutoff the load in case of low battery voltage. sir this circuit work propely on software and alone but when i make the combine pcb of these circuit a problem occurs which is our protection circuit not works , voltage of charging circuit meets with protection circuit voltages. kindly give me some tips to solve this problem?

On April 20, 2015 at 12:19am
Andre Van den Wyngaert wrote:

to Roni,
JYC 7.5 is lead acid in my opinion. OK, the acid is actually acid gel, but it behaves like a lead battery. Size is approx 150x95x65mm, right?
So in that case there should be no problem when you replace it with a 100Ah lead cell, like a car battery.
If you are sure it is not a lead battery, please provide the exact model number of the UPS and the text on the battery.

On April 20, 2015 at 12:38am
Andre Van den Wyngaert wrote:

to Aatif Anwar,
that will be hard to tell without any schematic to look at…
I am not sure if I understand your question: so you have made a charger, and it works OK. Then you have a circuit that cuts the load in case that the battery voltage goes too low - and it works OK too. Then you connect both to the battery, and it does not work.
- maybe the battery voltage stays above the treshold, so it is never too low?
- maybe the protection circuit reacts as it should, but at the moment the load is disconnected, the battery voltage immediately increases because the charger is connected, so the protection switches the load ON again. Maybe it quickly turns ON and OFF without you noticing it, like an oscillation. You can check with an oscilloscope. In that case, you should add some hysteresis to the protection circuit. E.g. below 11V it switches OFF, and it switches ON again only when it goes above 13V. (these values are only an example; real values depend on your application an battery).

On May 6, 2015 at 3:30pm
othman issa wrote:

i want to know the method of discharging the battery

On May 7, 2015 at 9:40pm
Aatif anwar wrote:

Hello sir i have make a smart charger for lead acid battery which works properly and normal condition and float charge condition. now i want to make deep discharge protection circuit for lead acid battery because in lead acid batteries there is no protection circuit i want makes the protection circuit using mosfet and comparator circuit , initially i have make a protection circuit for deep discharge by mosfet which cutoff the load below 10.5V the problem occurs here is battery voltage and circuit voltages is meet which each other and deep discharge circuit is not working properly i need your suggection what can i do these two voltage can not meet which each other

On May 8, 2015 at 12:16am
Andre Van den Wyngaert wrote:

to Aatif Anwar: Hi there, I still think you need to add hysteresis like I desscribed above. A simple comparator won’t work. It must get positive feedback, so that the difference between switching on and off is at least 2 volts, maybe even 3 volts. In your case, at 10.5V it would turn off the mosfet, and only turn it back on when the voltage has increased to 13.5V.
If that does not work either, you can make a workaround by adding a timer circuit that gets triggered at 10.5V by your comparator. Then an off time of x minutes/hours starts with your load off, and the battery gets time to charge. Success!

On May 13, 2015 at 6:50pm
Geoffrey wrote:

I have a bank of 10- -6v L16p Trojan batteries wired to output 12v—series/parallel; 
420 Ah per string x 5= 2100 Ah.

They are a year and a half old, I purchased them second-hand and they have self-discharged quite low, less than 10v.  per series pair.  I don’t  have any load connected at this time so my concern is solely to recharge them to 13-14v range.

They are currently off-grid with 700 watts from solar panels available for charging. I have about 3-3.5 hrs direct sunlight per day.

What would be the formula for calculating the time necessary to bring them back to a fully charged state?
I’m thinking it would be quite some time with my present setup since Trojan says the battery bank can handle 110 amp charge rate.


On May 14, 2015 at 11:14am
Bob Kondner wrote:


Yes you want to get them charged. I am surprised they dropped to 10V after 1.5 years. That is a long time but I would not have guessed at that level of drop. Depends very much on temp.

What you need to do is allow the batteries to charge until their voltage hits a “Peak” value. After that you need to reduce charging current. That is how most “Multi Stage” commercial charger operate but these chargers can control the charging current, most solar chargers can not do this.

What you need to do is monitor the charging current and battery voltage. When you have low charging currents the “Peak” you want to detect is lower. From your numbers you will get about 200 Ahr of charging a day so your 2100 Ahr battery will take 10+ days to charge. Like the commercial chargers you want a “Multi Stage” charging process but your stages will each span periods of no charging (night).  This interrupted charging might reset your charger logic which is not good.

To control charging current you will need to insert a power resistor between the battery and solar panel. The value will be the (Peak panel voltage - 13) / Low Level Charging Current. You might need two such resistors,  one resistor value for each phase. A linear regulator will be better but it needs to dump several hundred watts.

You also need to consider temperature. That peak voltage must be adjusted higher when cold. The other issue is the allowed length in time of charging phases.

Another consideration is discharge into a load. I short light discharge should not affect your chargers status. A larger load should reset the charger state.

And you final concern with peak voltages is gassing. If you want to reduce water requirements then the peak voltage is reduce (again using temp) and the battery is allowed to slowly soak charge.

I have a smaller battery, 2 pieces of 350 AH Rolls in series. The charger is 50 Amps with a peak of about 14.4 followed by reduced current to 13.3V. At 13.3 the batter is float charged. It takes several days to get the last 10% of charge into the cells. I monitor the charged level using specific gravity of the acid. I can see increased charging during the sever days. If I hook up a 1 amp charger to “Speed Things Up” the voltage rises high and I get significant gassing. I would rather not gas out my water so I allow it to float charge slowly at 13.1. After a week I disconnect the charger and let them sit for 3 to 6 months. Every 6 months I do a complete charge/discharge/charge cycle.

Bob K.

On May 18, 2015 at 5:57am
Mohammed Saleh wrote:

Your site is a good reference for battery malfunction .Keep me in touch to be update for more infos.

On May 19, 2015 at 4:12pm
T-VIRUS wrote:

I have 2 Trojan J305H-AC batteries linked in series for 12V operation in my battery bank I got them for scrap value from the scrap metal dealer (I get all my batteries from there mostly AGM batteries and 90% of them are still perfect)
But when I charged them initially 2 cells on each battery were gassing and the other cells were just starting to bubble a little bit after an overnight charge and the batteries were starting to get a bit warm
When I disconnected them the voltage went from 14V down to 13.6V immediately
And about an hour later it dropped to 12.6V
When I connect a 700W load through an inverter it lasts for about a min before it goes into low battery shutdown

Do you think it’s possible to recover them or would it be wise to cash them in and try again?

On May 22, 2015 at 10:13pm
GEORGE Douroudakis wrote:

My question please.
Can a lead-acid battery be charged while it is in use (i.e in a radio devise ????)
Why if not ??
Thanks for the most excellent, most excellent site.

On May 26, 2015 at 1:55am
Andre Van den Wyngaert wrote:

to GEORGE Douroudakis:
yes, that is perfecly possible. Actually this is the way many UPS work: the battery is kept at a fixed voltage e.g. 13.8V by the charger. In the mean time the 13.8V voltage is used for the load, e.g. a converter to 230VAC. If the mains voltage fails, the charger stops working, but the battery still feeds the load without any interruption.
Only requirement is that the charger is powerful enough to charge the battery AND feed the load at the same time.

On May 28, 2015 at 5:28am
Ali wrote:

I have a Panasonic VRLA 200AH battery connected to a MicroTek Inverter, the inverter has two options, High(14.2) and standard (13.8)charging, which option is better for the battery?

On May 28, 2015 at 8:35pm
lukman ahmed wrote:

i have a question for lead acid battery about the sulfer.
when a battery fully charged then how can creat the sulfate in a positive plate.and then how to remove this sulfer from the battery.

On May 30, 2015 at 10:56am
Bill wrote:

Voltage difference during series charging: a bad sign?  A series pair of identical brand and model 18AH 12V VRLA batteries, purchased from the same vendor at the same time,  power my stand-alone driveway gate opener. The batteries are charged by a 75W 24V solar panel via a PCM solar charge controller.  With ideal illumination and the controller not in its “float” charging phase (i.e., near-maximum charging voltage applied), I see substantially different voltages across the two batteries.  One shows around 13.46V, the other 14.59V.  Does this indicate a defective or worn-out battery?  If so, which one?

On May 30, 2015 at 1:49pm
Bob Kondner wrote:

If the batteries are sitting with open circuits on their terminals then that 14.59 sounds very high. I suspect there is a small charging current and the two batteries are acting differently. That 14.59 is high enough to start gassing and you don’t want that on a prolonged basis.

Once charged even a very small current will keep the battery voltage high and with small currents the voltage on different batteries in series could be very different.

Put a current meter in series with your batteries and see what kind of current is going into the batteries. The 18AH batteries you mentioned are a little small and the charger should “Float” them at about 13.3. V. If you find ANY current going into the batteries once they are full charged then they are being over charged.

Bob K.

On June 7, 2015 at 8:08am
Geoffrey wrote:

On May 14, 2015 at 11:14am
Bob Kondner wrote:
Yes you want to get them charged. I am surprised they dropped to 10V after 1.5 years. That is a long time but I would not have guessed at that level of drop. Depends very much on temp.

What you need to do is allow the batteries to charge until their voltage hits a “Peak” value. After that you need to reduce charging current. That is how most “Multi Stage” commercial charger operate but these chargers can control the charging current, most solar chargers can not do this.
What you need to do is monitor the charging current and battery voltage. When you have low charging currents the “Peak” you want to detect is lower. From your numbers you will get about 200 Ahr of charging a day so your 2100 Ahr battery will take 10+ days to charge. Like the commercial chargers you want a “Multi Stage” charging process but your stages will each span periods of no charging (night).  This interrupted charging might reset your charger logic which is not good.

To control charging current you will need to insert a power resistor between the battery and solar panel. The value will be the (Peak panel voltage - 13) / Low Level Charging Current. You might need two such resistors,  one resistor value for each phase. A linear regulator will be better but it needs to dump several hundred watts.

You also need to consider temperature. That peak voltage must be adjusted higher when cold. The other issue is the allowed length in time of charging phases.

Another consideration is discharge into a load. A short light discharge should not affect your chargers status. A larger load should reset the charger state.

And your final concern with peak voltages is gassing. If you want to reduce water requirements then the peak voltage is reduced (again using temp) and the battery is allowed to slowly soak charge.

I have a smaller battery, 2 pieces of 350 AH Rolls in series. The charger is 50 Amps with a peak of about 14.4 followed by reduced current to 13.3V. At 13.3 the battery is float charged. It takes several days to get the last 10% of charge into the cells. I monitor the charged level using specific gravity of the acid. I can see increased charging during the several days. If I hook up a 1 amp charger to “Speed Things Up” the voltage rises high and I get significant gassing. I would rather not gas out my water so I allow it to float charge slowly at 13.1. After a week I disconnect the charger and let them sit for 3 to 6 months. Every 6 months I do a complete charge/discharge/charge cycle.
Bob K.

Hi Bob K.,

Ok, trying to sort out this information intelligently I have been re-reading several times.

We have the:

voltage Peak value
Multi Stage charge phases
Monitoring charging current and battery voltage
Lower charging currents the Voltage Peak is lower
Resetting charger logic
Peak Voltage/Low Voltage Resistors
One resistor value for each phase—-Phase—High/Low?

voltage Peak value
Most of the time my voltmeter indicates in the 13+ range, sometimes hitting 14v

Multi Stage charge phases
I am having troubles with sulfation of several of the batteries. The ones that can charge to the full 6 volt are off gassing more than I like, as a result of the sulfated ones not going to a higher charge. In order to lower the charge to avoid excessive off gassing I need to desulfate the problem batteries, temporarily remove them from the bank.

Monitoring charging current and battery voltage
Looking at my voltmeter and ammeter now before direct sunlight they are showing 12.6 & 1.8a. How is the 1.8a number factored in per hour?

Lower charging currents the Voltage Peak is lower
The relationship between volts and amps is something I haven’t completely grasped yet. Are you saying that the lower the charging current, the lower my voltage and vice versa? The lower my voltage the lower my current?

Resetting charger logic
Is charger logic the path a charger follows in the multi stage steps from bulk to float?

Peak Voltage/Low Voltage Resistors
Would the resistor values be one for high voltage and one for low current?



On June 20, 2015 at 6:02am
Mark wrote:

The first paragraph says, ‘Lead acid charging uses a voltage-based algorithm’ and then the second paragraph says, ‘Lead acid batteries should be charged in three stages, which are [1] constant-current charge, ...’

So is it voltage-based or current-based? The graph shows a constant 1A current for the first phase, but chargers are available that deliver 10A. If you have a system with say two 110Ah deep discharge 12V batteries how do you choose a charger?


On June 20, 2015 at 6:41am
Mark wrote:

The paragraph on ripple voltage ends with, “...limit the ripple to five percent, or 5A for a 100Ah battery.” Are we talking ripple voltage or current? In any case, 5A is not 5% of 100Ah, they are completely different units! If we’re talking ripple voltage then 5% will be 0.6V for a 12V battery.

On June 22, 2015 at 1:28am
Andre Van den Wyngaert wrote:

to Mark:
In my understanding as an electronics engineer, “voltage based charging” means that a voltage must be applied, and then the battery itself ‘chooses’ how much current it will draw, depending on its charge status. When the charge status is low (the battery is discharged), the current can be very high, so it must be limited. So it appears as a constant current charge, but actually it is a voltage based charge with the current limited. In this low-charged state it actually makes no difference. The current will stay constant at the limited value, and you will see the voltage raise gradually. At a certain point, the voltage reaches its limit (value is depending on the battery voltage and type) and cannot go up further; it is limited by the charger. The battery charges further, but since the voltage cannot increase anymore, the current now starts decreasing gradually. Here you see a constant voltage over the battery, and the current depends on the charge state.
A charger is chosen based upon the time you have to charge a battery. You can charge a big battery with a small charger, but it will take days to charge it. But you cannot charge a small battery with a large charger, since this will damage the battery. In the text it is stated that you can charge a sealed battery in 12…16h. Much faster won’t be possible without risk. But with a smaller charger you can do it in a lot more hours, which is allowed.
Voltage ripple and current ripple go hand in hand. With an electronic current limiting circuit, there is no ripple at all. But with a charger consisting of nothing more than a bridge rectifier and a series resistor, the ripple voltage and current can be quite important. 5% of 100Ah - OK, you got a point, but they mean: take the number of Ah’s and take 5% of that to get the allowed ripple current expressed in amps.

On July 7, 2015 at 5:15am
Inteliano wrote:

See a guide on a simple do it yourself at home Lead Acid Battery Charger Circuit at http://lifestyle-facts.blogspot.com/2015/07/lead-acid-battery-charger-circuit.html

On July 13, 2015 at 10:17am
Tim Kuhlman wrote:

I have a 12V 35AH SLA rechargeable batter I use on my golf trolley.  What battery charger should I be using on this (amp specs etc).  Many problems in the past with the trolley mfg supplied charger.

On July 13, 2015 at 3:36pm
Tim Kuhlman wrote:

As a follow on to my previous question re 12V 35 AH SLA rechargeable battery for my golf trolley.  It is a AGM type construction, not sure if this makes a difference as to what battery charger I need.

On July 23, 2015 at 2:11pm
aiyetan michael wrote:

hi everyone

On July 24, 2015 at 11:22am
wanek t. wrote:


what is the maximum operating temperature for a sla, without damaging it?
also, what is the maximum recommended discharge voltage, without damaging a sla?

thank you!

On July 24, 2015 at 8:08pm
Lawrence Coomber wrote:

This is a very strong forum with a long history of contributions on battery related technology. Unfortunately whilst the subject has evolved rapidly the introduction to the forum has not and does not reflect the current best practice design principles for modern design engineers to consider.

Battery charging algorithms should no longer be devised and implemented “externally” to the battery or battery bank but be “dynamic charging algorithms” derived by “smart charging circuitry” that communicates with the battery or battery bank in situ. Battery charging cannot be efficiently and effectively managed without the charging circuit “knowing precisely” the SOC of the battery at any time and also the DOD that the system designer has specified as “not to be exceeded”.

I hope the forum can focus more on this critically important subject of “dynamic charging algorithms.


On July 25, 2015 at 10:44am
Bob Kondner wrote:

  I do not totally agree with you. Knowing the state of charge is very useful information for battery chemistries like NiCd and NiH but not for all. For example consider a Li Ion with a max cell potential of 4.2V during charging. Except for the logic of detecting a bad battery there is not much you can do except charge to 4.2 volts. A flooded Lead Acid is similar with the large rise in voltage during final charging. Though, even with Lead Acid, knowing the state of charge as full can help with getting the last 10% of capacity charged without extensive overcharge. At higher “Bulk” charging rates SOC is more useful.

So yes knowing the state of charge can help charging a battery to maximum capacity quickly its usefulness is minimal. I would suggest SOC is a second order affect.

What you did not mention, and you might have just assumed this, is battery temperature. I have found adjusting charging logic based on battery temperature to be more important than SOC.

Bob K.

On August 12, 2015 at 10:57am
Aba Peter wrote:

Hi all. I’ve tried to follow your very interesting conversations and comments. I am a medical missionary( so do keep your responses to a level a physician can understand and not the high tech stuff for the EEs).  I work in a somewhat remote location where power has to be generated by gas plant.
We have a 48V 5kVA inverter with a bank of 12 200AH batteries in parallels of 4 each. Last week, 4 of them became very hot and swollen and I had to disconnect them. The inverter turned out to be producing 91V instaed of 48V.
My question is ” is it safe to still use these batteries and can they be charged without any hazard to anyone? Also how do you check water level in sealed batteries?
Regards and keep up the good work.
Finally, What’s yoour email Andre?

On August 12, 2015 at 11:27am
Bob Kondner wrote:

Sounds like you had one battery fail shorted and the other batteries overcharge the heck out of the one stack with the shorted battery. I would be very suspect about the swelled units, I would guess they are very much damaged and putting them back into the setup would be dangerous.

I do not understand your comment about the inverter putting out 91V and not 48V. I was thinking your inverter was an AC output inverter. But perhaps you were referring to the charging inverter? A 91V output from a charger for 48V batteries indicates a failed and dangerous charger.

You had some type of failure event, someone needs to verify that each component is ok and functioning. At that point you can reconnect the system with any repaired / replaced failed components.

Bob K.

On August 26, 2015 at 6:05pm
Cory richsrd wrote:

Do I need to charge a new 12 volt 5 amp sealed lead acid battery?

On September 7, 2015 at 5:52am
Andre Van den Wyngaert wrote:

Cory richsrd,
Lead acid batteries don’t like being “empty”; they get damaged. So they are never sold empty. When you measure the voltage of the new battery, you should find 12.5V or so. If you find only 12V or even lower, you should bring it back to the shop and request a good one.
It wont do any harm if you charge it first. The charger will take care that it is properly charged and not overcharged, even if you start with a half-full battery.
Don’t use lead-acid batteries until they are really empty; the voltage should always stay above 12V.

On October 7, 2015 at 6:57pm
Mile Zawi wrote:

First of all, thank you for this great great website from which I’ve learned most of the fundamentals about batteries.

I wanted to ask you about a table I found on many batteries’ data sheets, which is the charging methods. Now I’ve read the this whole article and understood how to know what a certain C rating means, but can you explain the following to me?

Constant Voltage : -0.2Cx2h+2.4~2.45V/Cellx24h,Max. Current 0.3CA
Constant Current:  -0.2Cx2h+0.1CAx12h
Fast:      -0.2Cx2h+0.3CAx4.0h

I think I can understand the part after the plus sign, but I don’t get the part before the “+” sign? And what is the difference between “C” and “CA” ?

On October 8, 2015 at 9:27am
nigam wrote:


On October 13, 2015 at 5:15pm
Octavia Yon wrote:

My company is testing a new system called Vebar on our 125 chargers to predict the problems occurring within our forklift batteries. I would like to know of similar companies with the same technology tat can read the temperature, sulfation levels and electrolyte imbalances as well as overcharging times. We receive a dashboard but it is on a one week delay so we are currently trying to track specific problem batteries with specific chargers. our batteries range from 24 to 48 volts and are from many manufacturers such as Exide, Hawker, Deka ..etc. any info on whether this company is the best?

On October 18, 2015 at 10:50pm

can one charge acid Lead batteries and still be using it at the same time while using it and the charger will still be charging it , is it possible?

On October 20, 2015 at 2:55am
Andre Van den Wyngaert wrote:

@ Agada Idoko Joshua:
You can charge a battery and keep the load connected. So the power supply will charge the battery and power the load. If the power supply fails, the battery will power the load.

If I take your question literally: current can run in only one direction at a time, so a battery will either charge or discharge.
Best regards,

On October 22, 2015 at 7:13pm
Vaibhav wrote:


We do not have facility to provide charging current of 30 Amp to 300 AH battery so we are trying to charge the battery at constant 10A. Will it charge the batteries properly? I will keep the charging for long

On October 23, 2015 at 12:33am
Andre Van den Wyngaert wrote:

charging with 10A won’t do any harm in my opinion. But it will take 3 times longer to charge than with 30A. But it will be equally charged at the end.
Best regards,

On November 11, 2015 at 11:23am
Germain wrote:

Hi John,

Many thanks for all those informations, I’ve spent or rather gained a lot of hours reading ! grin

Please may I ask you some questions about charging a Ca/Ca battery, as:

1) What are the proper voltages for the boost and float phases to stay on the left side of your table 2 above ?

2) What is recommended duration for the boost phase ?

3) What are the recommended voltage and duration for the monthly equalization ?

As you guess, it is for a solar installation with a programable controller…

Thanks in advance for your appreciated help and kind regards,

On November 11, 2015 at 11:28am
Germain from Geneva, Switzerland wrote:

Sorry if my previous post was directed to John instead of André... wink

On November 11, 2015 at 12:24pm
Germain from Geneva, Switzerland wrote:

Sorry again but I forgot to specify that it is a 12-volt battery, shame on me !

Anyway many thanks to each person responding to my simple questions…

On November 14, 2015 at 7:57am
RonB wrote:

can I charge different 12V lead acid batteries that are wired in parallel to deliver 36V on my cart, with a 12V 10A charger

On November 16, 2015 at 7:49pm
Vaibhav wrote:

Hi All,

I am happy that I have successfully charged by batteries with a good gravity…

On November 19, 2015 at 8:05pm
Bob King wrote:

Hi, I use two package of Lead Acid battery(Panasonic LC-R127R2) as the power source to supplement a medical device, now I am on the software development of the power management board to realize a functionality that monitor the SOC(state of charge) and send the value of SOC to a computer via UART periodically. the software has already the capability to measure the (1)battery voltage(2)Charging current during charging(3)load current during discharging. Does anyone has a good solution to realize it?
P.S. The source code I am using comes from a previous project which is also used for a power management board, it’s already has a formula in software to estimate the SOC, here it is, during charging, SOC= 100%(1-(Vmax_- Vbatt + Ichrg*Ro)/2.5V)    (Vmax_ = 25.5v, Vbatt is the value of battery voltage measured by SW, Icharg is the value of charging current measured by SW), during discharging, SOC = 100%(1-(Vmax -  Vbatt-Iload* Ri)/2.5V)  (Vmax = 25.5v,Iload is the current of load measured by SW). However, I don’t know the principle behind the formula and if it’s good enough to use for estimation of SOC…..

On November 20, 2015 at 7:51am
Bob Kondner wrote:

  Battery voltage is a poor indication of state of charge, best you can typically do is start charging and watch the battery voltage. At least then you know when it is full.

I did a LOT of work with battery charging, I have a lot of code that goes into PIC processors. What I did and really helps with state of charge is knowing the battery capacity and monitoring battery currents. You do not need super accurate values of current as capacity is not a “Precision” parameter in the first place. And any time you play with a battery voltage you need to consider battery temperature. I have some nice code and tables for thermistor linearization. There are low cost 0.5% thermistors out there, they are used in the digital thermometers like what you see in drug stores. These inexpensive sensors and can be found at Digikey and Mouser. I go some other projects now but perhaps I can help.

With temp you can also approximate self discharge.

Pull down: http://www.sunduino.com/updates/SunD_Demos.zip as it has a lot of hardware and software info.

Bob Kondner

On December 9, 2015 at 10:55pm
Sherman Johnson wrote:

I recently put a 3 amp Battery Tender on a typical lead-acid auto battery.

The voltage prior to connecting the charger was 12.42V.

All charger indications were normal.  What surprised me was that the voltage quickly (within ~2 min.) increased to 14.5V and the charger switched to absorption stage, as indicated by the flashing green LED.

2 minutes seems like a very short amount of time for the charger to remain in the bulk charging stage when the resting voltage of the battery was just 12.42V.

Any thoughts or ideas?

Thank you.

On December 15, 2015 at 7:44am
mxolisi wrote:

my 12volts suv v6 battery has very little water, should i pour acid water or demineralised or both?




On December 16, 2015 at 8:36pm
Bob King wrote:

Mr. Kondner,
Thank you for the quick response and sorry for keeping this topic updated late because I’m busy with some urgent stuff.
As you mentioned that the battery voltage is a poor indication of SOC(during charging),so by your experience, wut’s the better way to measure the SOC? and measure the DOD(Depth of Discharge)during discharging?  Use the integration of current over the charging time?
Here is my situation,I need to measure the SOC and display it in LCD during charging as well as the DOD during discharging.

On December 17, 2015 at 6:08am
Craig wrote:

I’m looking to do similar to you bob and to measure the SOC in charging, discharging and idle states on a battery cart.
My confision is where I start to calculate the state of charge, do I assume the battery is fully charged when its installed in the cart? (and ensure this is true where possible)
And how would I compoensate for say self discharge and temperature and their effect on the amount of charge the battery is able to provide or recieve? I’d imagine I’m looking for a temporary value of what Ah i can provide at this temperature at this age etc in relation to my current charge?

On December 17, 2015 at 6:10am
Craig wrote:

In addition to above, I am measuring the current of the charger and load in my software, as well as the voltage of the charger, batteries and load.

On December 17, 2015 at 12:23pm
Bob Kondner wrote:


Yes the starting point is a problem grin

I keep a bit called NEW BATTERY. When a battery is disconnected and latter reconnected NEW BATTER is set and it modifies charging logic. I decided long ago that once a system has been powered up, and a battery is re-connected, it is very likely the same battery being connected. I keep a copy of the gas gauge (current battery charge) in EEPROM and on a re-connect I grab this value and jam it into the charge monitor. I tell users it is important to do a complete discharge followed by a full charge when they REPLACE a battery. That syncs the charge monitor to the battery. When charging you can always detect when a battery is “Darn Close” to full so I use that event in all my logic.The EEPROM idea covers same battery reconnects. These two processes do a good job at solving 99% of what user might do.

It is important to make certain your processor is powered and running at all times. (Sleep Modes) That become a serious engineering task as you need to keep EVERYTHING down to the 10ua or less drain area. You also want a “Freshness Seal” (about 100na of draw) if you want an Li Battery to remain fresh over years of storage. And if you see a really low battery for a long period they you want your design to re-seal the freshness seal as even a 10ua load will take a low battery voltage to zero.

I also added a logarithmic self discharge function that uses battery temperature and I considered using cell voltage. Problem is cell voltage vs self discharge is not specified well, if at all. Best I could find is temperature related self discharge.

So how far do you really want to go? There are many things you can do but not all make sense for your specific application.

Bob K.

On December 17, 2015 at 7:19pm
Bob King wrote:

Then how do you implement currently for calculating the SOC?

On January 21, 2016 at 9:52pm
Bob Sanco wrote:

Geezzz I can see that it will be a full time job to answer all these questions even just the ones that make sense.  No thanks….  I am ok after all….

On January 24, 2016 at 6:02am
umesh wrote:

Is it possible to charge 12v,75Ah lead acid battery directly by solar panel of 74Wp,19.6Vp?

On January 24, 2016 at 7:46pm
DJ Sailor wrote:

My whole house generator uses a flooded lead acid (non-sealed) for starting. A 2amp heater was installed (under warranty) to prevent moisture condensation on the brushes of the A/C generator’s armature (which would cause a fault preventing starting).

Do to the long run (about 80 ft one way) and thin gauge wire from where the battery charger is located to the battery, when the heater is on (below 38 degF), the voltage at the battery drops from 13.4v to 12.8 to 12.9v. Since the generator (when running) charges the battery at 14+ volts, the 4 amp battery charger just needs to maintain the battery’s condition.

My question: Is this low voltage during cold weather going to be a problem in maintaining the battery’s condition during winter or its longevity?

Thanks in advance, DJ

On January 25, 2016 at 2:09am
Andre Van den Wyngaert wrote:

I see that a 74Wp panel has a short circuit current of 4.55 Amp approx, and an open voltage of over 19V.
So if you connect it directly, it will work, as long as the voltage stays below the maximum for the battery. As soon as the battery voltage reaches its max voltage, you should disconnect manually. Max voltage allowed: see article above… will be 14V or somewhere near, depending on temperature and other conditions. If you don’t disconnect, you can destroy the battery.
Better and safer solution will be some charger circuit between panel and battery.
See Youtube movie: “Charging a Car Battery with a Solar Panel and Charge Controller”
Best regards,

On January 25, 2016 at 3:06am
Germain wrote:


Many thanks for all those informations, I’ve spent or rather gained a lot of hours reading !

Please may I ask you some questions about charging a 12v Ca/Ca battery, as:

1) What are the proper voltages for the boost and float phases to stay on the left side of your table 2 above ?
2) What is recommended duration for the boost phase ?
3) What are the recommended voltage and duration for the monthly equalization ?

As you guess, it is for a solar installation with a programmable controller…

Thanks in advance for your appreciated help and kind regards,

On January 28, 2016 at 5:18am
shihab sakib wrote:

i have 12v lead acid battery. please someone con tell me why my battery discharging so fast? and what is the proper reason of this quick discharging?

On February 1, 2016 at 7:43pm
Cole wrote:

Here at work we use 36v forklifts with massive lead acid batteries.  I’ve been informed that we may start to use an opportunity charging method (charge a little here and a little there while the lift is not in use, say an hour or two at a time).  As a long time electric rc enthusiast i was trained that batteries have a limited number of charge cycles before declination of preformance, from li-ion in our phones to large industrial ni-zn and lead acid. 

My question, is it true that batteries such as water filled lead acid are limited in the number of charge cycles before performance decline whether it be charging from 60 to 75% or 10 to 100% as 1 cycle

On February 1, 2016 at 11:42pm
fong wrote:

I have one normal car battery and one deep cycle battery in my 4x4, which is parked up for lengthy periods.
I have a simple arlec 4 amp charger that switches on via a timer for 15 minutes twice a day 12 hours apart, the battery’s are connected in parallel.
This seems to work out well but is it the right thing to do.
An expert opinion would be great.

On February 2, 2016 at 7:24am
Murali wrote:

Can Some one plese tell me exactly how many litres of distilled water must be added to 150AH inverter Battery where the distilled water is critically low to fill it to the desired level

On February 10, 2016 at 11:04am
Arash wrote:

Hi can some one till me 12/v 220ah how maney ampere is thx

On February 20, 2016 at 7:54am
Ejohnb wrote:

Hello, I just imported an LPG steam car washing machine from China to Nigeria and the machine has 4x12volts battery in it,the charger is also rated 48V,2.8A but each time I try to charge the battery, it doesn’t and it’s getting me insane as I need it to work so as to start up my business and the manufacturers are not responding. The power rating in Nigeria is 220V,could this be why it doesn’t charge? Please I need help asap.
I’ve been thinking of buying a step up or step down but now I Dont really know what to do anymore. Please help.  Thanks.

On February 21, 2016 at 10:13am
Jiffer wrote:

First thing to check is if you have correctly configured your batteries in series because if your charger is  48v  than your batteries must be set up in series which would make 4 x 12v equalling 48v—- positive of one battery to negative of next, negative of first battery to positive of next. This way you increase 12v to the needed 48v.

Second would be to check your battery’s individual voltage. It should be at least 12.0 or higher to start taking a charge. Anything less than that might indicate the batteries have set around to long without a charge and have started to sulfate from self-discharge. It might be able to come back to life from the 11.0v + range but it can get kinda iffy.

A real tell-tale indicator of your battery’s health is specific gravity taken with a hydrometer. This will give you an indication of what percentage the sulfuric acid is in your electrolyte. That is what provides the chemical potential for electricity generation. If the individual cells read low on the hydrometer than that would mean your battery is in trouble.

Have you closely followed the manufacturer’s guidelines on how to wire up the connections of the battery? I would go back to ground zero as if it is the first time you have hooked everything up and make sure that you understand the way things are connected and don’t deviate from the instructions. 

If you have the wiring correctly positioned, than it is your batteries at fault. If your batteries all read within their specifications than I would check out the output of your battery charger to be sure it is delivering 48v+. You can do that with a simple multimeter set on DC, probably in the 200v range.

I would make sure the charger is meant to operate on 220v. There should be information on the charger that specifies what the electrical input should be: 120 or 240v (220- same as 240-just old school label basically). You have to be sure that it matches your country’s setup of 220v or it won’t work.

On February 21, 2016 at 10:37am
Ejohnb wrote:

Wow! Thanks @ Jiffer. I really appreciate it. The issue is that the battery is inbuilt and I can’t see the connections and the machine is heavily sealed. On the other hand, I’ll have to confirm two things like you just mentioned, which is to be sure the charger was made to function at 110 or 220v and to confirm if the chargers output is actually 48.
As for thr manufacturers part,  I’m in Nigeria and the machine wasimported from China, I’ve written so many mails to the company and trued calling all to no avail, worst of all the instructions on the charger are written in Chinese. So I’m currently at a fix. I’ve also been searching for someone will same or similar machine over and Ive not had any breakthrough yet.
Anyways, Thanks once again.  I appreciate

On February 21, 2016 at 7:15pm
Jiffer wrote:

If you could find a service door on your machine to access the interior it would help to demystify your conundrum. Without being able to visibly inspect your batteries you really cannot be sure if everything maintained it’s integrity during transportation. 

Can you take a reading on the voltage output of the batteries? I take it since they are not easily accessible they are sealed lead acid.

What is the make and model of your unit?

Any other symptoms or related malfunctions?

On February 24, 2016 at 8:36pm
Sherman Johnson wrote:


Does the mfr have a website?

On February 25, 2016 at 9:00pm
Faizan wrote:

Sir i have 1 Paison pro bike used 12 Volt battery but i do not know battery charging amp

On February 27, 2016 at 10:45pm
Michael Callander wrote:

Hi any who can help me, let you know about I have a dream about, let you know that I have Westport trike 20: kent and also 48 volt dc ebike 1000 watt E-bike. ok I did not planing buy yet, first my question for you ok how is work?
Harbor freight toll Gas motor 6.5 hp can use alternator or generator charge to 4 pc 12v 12ah= 48 v 12 ah? if yes what kind alternator or generator tell me how is work? My dream E bike can running from battery charge like long drive no stop keep going how?

On February 28, 2016 at 9:43am
Solar Car ENSMR wrote:

Hi ! can anyone tell me why the charge current of the battery fluctuate
i have an acid batteries ( 4* 12 =48 V ) and i have a solar pannels that gives me 17.3*3=52 V , and i use a regulator (MPPT) to which i hook my batteries , my solar pannels and a DC motor ( 3000kw)
the problem is that when i have 3 panels in series in parallel with 3 other panel in serie
i have a current that reaches 5.6 A+5.6A= 11.2 A , the carge current of the batteries start to fluctuate

On March 5, 2016 at 5:29am

I want to know what is the current drawn by VRLA Gel battery in float mode . When should the battery be put in boost mode while under float mode . I can measure the battery voltage and current both .

On March 5, 2016 at 8:39am
Tele wrote:

Hi,i bought new 12v 7.5ah lead acid batteries for my rechargeable fan. Since i was told to charge it for 20hrs i did a parallel connection to my old battery which is 12v7.0ah so it could charge,but i diconnected it when i wanted to use the fan. Now its been 20hrs. I connected it irectly to the fan. It came on for just 3minutes then went off. I tried it after a while without charging it and it did the same thing. Is the battery bad? Could it be a connection problem?please HELP!!!

On March 7, 2016 at 2:27am
Andre Van den Wyngaert wrote:

If it works for a few minutes, I think the battery is not bad, but not charged. Since you connected them in parallel, your charger must have terminated charging for some reason. Since you bought a new battery, I assume your old one is getting defective - maybe the voltage is too low. This can prevent the new battery from charging, because the voltage never gets high enough. When in parallel, both batteries get the exact same voltage, but different currents.
I guess it is best to simply install the new battery into your fan, and then charge it. No parallel connection with the old one.
Good luck!

On March 7, 2016 at 12:40pm
Tele wrote:

Thank you @Andre Van den Wyngaert. I’ll try that.

On March 8, 2016 at 9:03pm
salah wrote:

I have 165 cells - 1.2 vdc are connected in series, can I replace by 15 batteries 12 vdc

On March 9, 2016 at 2:01am
Andre Van den Wyngaert wrote:

1.2V x 165 = 198V.
12V x 15 = 180V and fully charged 13V x 15 = 195V.
Looking at voltage: yes, it will work.
But 1.2V is probably NiCd or NiMH; and 12V is probably lead, so your charging circuit will need a change…

On March 9, 2016 at 2:07am
Germain wrote:

Hello André,

Please could you answer to my question from November 11, 2015 at 11:23am just above ?

Thanks in advance and kind regards,

On March 9, 2016 at 2:39am
Andre Van den Wyngaert wrote:

@Germain: I would love to, but I am only a reader of these articles and can sometimes help with some advice on electronic circuits. I would have to look up all your questions myself, and probably make mistakes since I might misinterpret your situation. Depends on battery size and usage conditions.

On March 9, 2016 at 6:09am
@André wrote:

Thank you anyway for your fair answer !

It is sad we cannot found a lot of informations about how to charge these kind of Ca/Ca batteries because they are replacing more and more frequently the ancient Lead ones, for our vehicules at least…

On March 9, 2016 at 6:13am
Andre Van den Wyngaert wrote:

is this something: http://jgdarden.com/batteryfaq/carfaq9.htm
There is a CA/Ca curve when you scroll lower…

On March 9, 2016 at 11:09am
Germain wrote:

@André: thank you, I was aware of it, but halas some other curves on other Web sites show different voltage values…

On April 12, 2016 at 1:45am
Philip Beekman wrote:

How fast can I charge a flooded lead-acid battery? I have 6V 235Ah battery which I normally never discharge below 50%. My charger can provide 80 Amps, which is C/3. Will it damage the battery if I charge at this rate up to 70 or 80% (keeping Voltage below 7.2V), and then continue charging at a more moderate rate?

On May 1, 2016 at 7:55am
Ainuddin wrote:

can charge 12 volt batry with connect a 140volt altinetor that is running 1800Rpm

On May 16, 2016 at 9:35pm
Mayur wrote:

I have a 12v, 100Ah, heavy duty battery.

1.what is the minimum discharge voltage?
2.What are safe n quick discharge methods?
3.What considerations should I make while charging it with 12v, 10A Battery Charger?
4.How should I discharge it using a DC load bank of 45kW(electrical calculation)?
5.Battery aslo shows charging current 6.5A. what does that mean? According to it what precautions should be taaken for charging n discharging of the battery?

On May 16, 2016 at 9:36pm
Mayur wrote:

I have a 12v, 100Ah, heavy duty battery.
1.what is the minimum discharge voltage?
2.What are safe n quick discharge methods?
3.What considerations should I make while charging it with 12v, 10A Battery Charger?
4.How should I discharge it using a DC load bank of 45kW(electrical calculation)?
5.Battery aslo shows charging current 6.5A. what does that mean? According to it what precautions should be taaken for charging n discharging of the battery?

On May 31, 2016 at 8:04am
Khayrul Bashar wrote:

I need Lead Acid Battery Specification in Jis Standard. Please Mail me if you have.35 my email address basharsel@gmail.com

On June 6, 2016 at 12:30pm
Joe Elliott wrote:

Maybe someone here can help me with a question I’ve been struggling with for years—how do I know when a lead-acid battery is fully charged using a crude (transformer + rectifier) charger that’s significantly undersized for the capacity of the batteries?  (For example, it will barely supply 0.1*C worth of current to a fully-discharged battery—by the time it approaches the battery’s recommended charging voltage the current has fallen to like 0.005*C.)  Is there a formula by which I can calculate a termination voltage for a given C-rate?  Or a way to figure out how long to let it continue charging after it’s tapered off to 2.4 V per cell and 0.006*C?

On June 8, 2016 at 11:47am
Anita Weiss wrote:

to Joe Elliott
there are plenty of formulas here at battery university
the terminal voltage varies with temperature. one method is when the battery temperature starts to rise. I would say to stop once the temperature reached 5ºC above ambient
This is for a battery that has been in a stable environment for 24 hours

On June 8, 2016 at 12:05pm
Anita Weiss wrote:

To Mayur
The minimum discharge voltage is always 10.5V for lead acid batteries
for safety: no sparks or flame near battery, charge or discharge
this means connect charger to battery first and 120/220V last

3.What considerations should I make while charging it with 12v, 10A Battery Charger?
it depends, is it a commercial charger or a homebrew?
you mentionned a 100Ah battery, 10A charging current is a very god value
however, it would be necessary to look at the charger’s output, and the ripple current should not exceed 5% or more precisely, should not exceed 5% of the C/10 value

4.How should I discharge it using a DC load bank of 45kW(electrical calculation)?
I don’t understand your question
you discharge the battery by using the intended load. And you need to stop at 10.5V as below this voltage, the wear on the battery severely aggravates

5.Battery also shows charging current 6.5A. what does that mean?
It should mean that 6.5A is going into the battery at that particular time.
there are different types of battery chargers on the market. A low cost 10A charger, would recharge a 100Ah battery in about 10~12 hours
a smart charger for that specific battery (much more expensive) will recharge the same battery in maybe 2 hours

On June 9, 2016 at 1:51pm
Joe Elliott wrote:

Anita - To measure a temperature increase of 5° above ambient, would I need a temperature sensor inside the battery, or will this be measurable from the exterior of the battery?  And can you point me to any of the applicable formulas?  I’ve done quite a bit of searching and can’t seem to find anything that applies to my situation.


On June 9, 2016 at 2:01pm
Ayle wrote:

I have 185AH Battry installed a heavy UPS for my home
I have adjust charging volt 13.8V
As the charger cut off the charging my Battry reads 12.9 volts which gradually drops to 12.35 volts in about 12 hrs and charger again starts automatically to charge battry and the Room temperature remains about 30℃
My Question is ,
1.  is my battry is over charged as i read in article that a fully charged battry reads 12.65 volts

On June 12, 2016 at 2:38pm
Jay wrote:

Hi all,

Was hoping someone could answer this question.

Is there any rule of thumb or guideline for the allowable voltage drop between the battery charger and battery terminals?

For my system, the battery float voltage is to be 135VDC. But if I have too large of a drop between the battery charger and battery bank, there could be a problem. Could an issue be that the battery will not float at 135VDC if the voltage drop is too much? Or would the charger simply output more current to compensate for the voltage drop in the cabling?

I was thinking that a 3% voltage drop is okay, but i’m not sure.


On June 14, 2016 at 8:13am
Anita Weiss wrote:

to Joe Elliott
generally lead acid batteries should be charged at a rate of C10. that is 1/10th the AH rating
while the battery is charging, the temperature is stable = ambient
when it is fully charger, the temperature starts to rise. 5ºC rise is considered the limit
of a healthy battery, I have seen much more on old batteries (hot spots on the outer casing) very hot spot
Of course an internal sensor is preferable, but life is life
Use a thermocouple probe, there is some compound, very similar to chewing gum where you stick the temperature sensing wire close to the battery surface
and wait 3~5 minutes for the sensor to stabilize

Concerning your charger, it is wiser to use a higher voltage with a series resistor
the output current is much more stable (due to line voltage variations, battery voltage etc. than a straight transformer)
as opposed to just a transformer with diodes

On June 14, 2016 at 8:26am
Anita Weiss wrote:

in an inverter set-up, what would be the effect on reserve capacity minutes if the load has ripple current of 28A

as oppose to if I put a capacitor in parallel with the battery and reduce the ripple to 14A
the ripple is near triangular shape and 120Hz

On June 14, 2016 at 8:37am
Anita Weiss wrote:

To Jay
how much voltage drop are you referring to?
It depends, is this a homebrew, or commercial charger?
generally voltage drop is not an issue
at 135v, you are talking 105V dead, and 135V full charge, this is 35V difference
the charger has to accommodate this variation, hence why it is “normally” not an issue

On June 14, 2016 at 9:36am
Anita Weiss wrote:

To Joe Elliott
I suggest you read this article
it may answer many of your questions

On June 14, 2016 at 4:05pm
Jay wrote:

Hi Anita,

Thanks for your reply. This is a commercial charger. Yes, 135vdc full charge and 105V end voltage. I calculated the recharging current to be about 75A, this results in the voltage drop in cables of about 4V. So with the commercial charger, should I be less concerned about this issue?


On June 15, 2016 at 1:10am
Andre Van den Wyngaert wrote:

To Anita:
no idea about the chemistry involved, but speaking pure theoretically the difference would be that with 28A peak currents, the losses in the battery are higher. Losses are current x current x series resistance of the battery. If resistance is a constant, then the losses are quadratic with the current.
Higher losses mean lower output voltage.
So if you have a regulated inverter that keeps its output voltage constant, it behaves as a constant power load. It will draw slightly more current at its input since it gets a lower input voltage.
Both effects will add up: more losses inside battery+ slightly higher load current.  So it will make a small difference. If you know the battery Ri (resistance), you could make a guess…

On June 16, 2016 at 6:40pm
Wilson wrote:

How do I telly if my 15 year old charger is still working well or at all ? Can I do this with a multi meter ??

On June 26, 2016 at 12:11am
Manoj wrote:

at one site there was 2Volt 300Ah ZTE battery and till Friday night there was 4.5 hour battery backup and there was city supply problem and we ran DG for whole night and in the morning when we stopped the DG immediately all equipment including MUX got down and we ran DG again and checked all battery of these two bank and got 5 Battery from two Bank was completely dead. what will be the technical reason behind this?

On July 7, 2016 at 7:11am
Anita wrote:

To Wilson
How do I telly if my 15 year old charger is still working well or at all ? Can I do this with a multi meter ??
Usually yes, but not always
what type of charger? automobile?
plug-it in, try-it out, if you have a meter, check if come current is coming out
(BE CAREFULL! no sparks near the battery)

some chargers (small, 2A) starts on their own, larger ones (2A, 10A, & boost) needs some battery voltage to start

sometimes there is no contact, due to rusted clips, broken wires…

On July 9, 2016 at 11:46pm
Alvin Mallia wrote:

I have a ride on car for my kid. It takes 2   6volts 4.5a valve regulated lead acid batteries. Recently my charger broke down and supplier does not have any spare. Please can you indicate what charger should I purchase and if there is on ebay indicate a suitable model

On July 11, 2016 at 9:21am
Jay wrote:

Basic question here.

If I have a switched mode rectifier rated 1000W, while charging a completely discharged battery (end voltage 105V), will the current output of the charger be 1000W/105V = 9.5A in this scenario? Or would it be dependent on the float voltage, if float is set to 125V, resulting in a current of 1000/125 = 8A ?

On July 12, 2016 at 5:42pm
Anita wrote:

To Alvin Mallia
Unfortunately, the answer is NO
the reason being that there are too many variables

1,the connector has to fit, 2; the electrical parameters have to match….
what I suggest is to go to a store where they sell those type of batteries

they could see what is needed. the parameters you need is 13.6V with 0.45 or 0.5A current limit. (no hick-up mode…)
stay away from intelligent chargers

if you have a multimeter, and have access to the terminals*, you could get almost any “linear” power supply, provided that the current limit is not more than 500mA
and watch the voltage, disconnect the charger when the battery voltage reaches 13.6V (30ºC) to 13.8 (20ºC)
* no sparks near the battery!

On July 12, 2016 at 5:57pm
Anita wrote:

To Jay
Jay, it does not quite work like that!
The battery is a very large capacitor (extremely large in your case)
What will happen, depends on the internal plumbing of the power supply
For example, a laptop power supply that is 19V at 90W can and will deliver 19V until 90÷19=4.73….Amps
Beyond that, at some point it will shut down and restart a while later. This is called hick-up mode protection
What you need is a constant current power supply, only lab power supplies or chargers have this feature. Nothing to do with switch mode!

So, the current could be 9.5 Amps or whatever the limit is set at
and it needs a voltage limit set at 135V (125 is too low, it will cause stratification and sulfating problem)

If it is a rectifier that is designed to charge batteries, it will work fine

your statement
if float is set to 125V, resulting in a current of 1000/125 = 8A ?

That is, the power supply will deliver 8Amps until the battery voltage reaches the set-point, then will taper off to near zero Amps
all this provided that the power supply (rectifier) is intended for charging batteries

On July 14, 2016 at 2:18pm
Marc saya wrote:

Can you help me configure my charger?
I have a 48 volt 3 stages charger.
I can adjust the voltage for going from constant current to topping charge and also for going from topping to float.
I have 4 batteries in seie each is lead acid 12V 200Ah and the ambient temperature is 30 deg C.
I have fixed the contant charging current to 30A for the first stage and would like to set correctly the voltage levels for topping and floating stages.
Thanks in advance for your help.


On July 15, 2016 at 6:03am
Anita wrote:

To Marc Saya
You need to consult your charger vendor as they are the only people who know how the internal plumbing of the charger works
How to set your charger depends on your batteries and the application, if flooded, AGM, gel cells.
The application such as lift truck where the electrolyte gravity would be 1.3 (very stressed-out application)
1.2 in a telephone system application (very relaxed application)
Generally 1.27 in automobile application (many cycles, shallow discharges but high energy demands)
And again different in an emergency power system, few cycles, deep discharges

You mentioned 200Ah batteries; this means the batteries will deliver 10Amps for 20 hours (not 200A for 1 hour. maybe 50 Amps for 3 hours when new)
And should be charged at a C/10 rate of 20 Amps, but again, only the system designer knows all the answers


On July 15, 2016 at 9:26am
Anita wrote:

To Jay regarding your June 12th question
Is there any rule of thumb or guideline for the allowable voltage drop between the battery charger and battery terminals?
The answer is yes, and the applicable rule is “it depends”

What you are asking is “what is, or how do I determine the ampacity of my wire/s”
How much current can conductors carry is a function of safety and electrical parameters

Generally at high voltages, operating temperature governs the limit, and at low voltage, voltage drop governs the limit

In the case of battery chargers like you are asking, other than safety hazards (fires) there is no voltage drop to worry about
Because at end of charge there is not much current, therefore, not much voltage drop if any

The safety issues still prevail. Such as installing wrong batteries, IE 36V battery in a 48V system…

For that reason, chargers and batteries systems should be designed with interlocking mechanism so that charging power is only available after a series of tests have been done

If you look at your cell phone or laptop batteries, there is normally no power available at the contacts until both units are properly connected together

Some of the criterions that governs what type of wire (wire alloys, and insulating jacket) is suitable are

For example, a train catenary (overhead cable) it has to resist abrasion, from a voltage drop point of view, it can glow red if that is acceptable
Some cables are made of steel for strength because they have to support winter ice
Some are made of aluminum because of their light weight, sometimes reinforced with a steel core for added strength
Some are bundled together with others in a hot conduit
Some need to resist twisting and pulling like telephone handset

On July 24, 2016 at 2:24am
don wrote:

this is the first time ive charged a battery. what does it mean if the needle goes up when charging .is it good or bad

On July 27, 2016 at 11:02am
Muhammad Zeeshan wrote:

I have a 12V, 185Ah battery and a 20amp charger for it. I want to know that:
1. How much energy in kWh is required to get the battery fully charged?
2. battery is attached to a 700W inverter. For how long would it continuousely supply AC current?
3. Can i calculate out put voltage V, amperes I and Watts W?

On July 29, 2016 at 1:25pm
Anita wrote:

Dear Muhammad
1 the answer to your question is it depends on any factors like what is the starting voltage…
Typically to get 100W out of a battery it needs about 140W of charge when the battery is new this relates to the battery efficiency. This efficiency will gradually diminish as the battery gets used.
It should take 10 hours or more to fully charge the battery
The charging current should not be more than 18.5A for your application. All that depends on what is the life expectancy.
For example, an emergency power system, which may operate 5 times in 10 years of service, would have very different design criteria than a solar power plant.

3 to calculate voltage and current, refer to Ohms law

On August 3, 2016 at 12:38am
Andre Van den Wyngaert wrote:

if the battery is empty, you need 185Ah*12V=2220Wh=2.22kWh theoretically. This result x 1.4 like Anita said, due to efficiency, gives you 3.1kWh approximately. But then there is also the efficiency of your charger. If it has 80% efficiency, your total energy bill will be 2.22x1.4x1.25=almost 4 kWh.  (1.25 = 1/0.80 for efficiency of charger).
2. When you consume the full 700W, you theoretically have 700/12=58 Amps charge current - quite a lot I think. You have 185Ah, meaning a charge of 1 amp can be delivered 185 hours. So 58 amps will last 185/58=3.2 hours. But this is theory. The less-than-100%-efficiency of the inverter must be taken into account. 80% maybe? So that is 80% shorter then…
3. For DC (battery voltage), V x I = W     so I = W / V   and V = W / I
W x hours = Wh (watthours)    One Wh = 1/1000 of a kWh kilowatthour
For AC (230V or 110V inverter output), output watts = V x I x power factor. Power factor depends on the load. A resistive load like a standard light bulb has a power factor of 1.

On August 4, 2016 at 8:29am
Anita wrote:

Only a field trail can answer some of these questions. Your questions are far beyond the scope of a forum like this
2) How long will the inverter supply output? Quick answer is, about 30 to 45 minutes

To charge the battery you need at least 13.6V preferably 13.8V and once in a while (twice a year 14.4V for 1 to 2 hours) when the batteries is/are new, more often when older
If we refer to BU-403 article, it states 12 to 16 hours charging time.
That translates to 185Ah/12h= 15 Amps and 11 Amps charging rate
So the charger output current should be limited to these values to prolong the battery life
One has to understand, every time we charge/discharge the battery we rob some of its useful life
How much? It depends on the chemistry and how deep. Generally at 10.5V the wear (or damage) is considered severe!

Regarding the charger’s efficiency (in terms of electrical voltage/current conversion) it depends where the prime energy comes from and a bunch of other factors

2) How long will the inverter supply output? Quick answer, about 30 to 45 minutes

The battery rating 185Ah means the battery will supply 9 Amps for 20 hours
Ah rating is always for 20h

If you plan to use 58A as calculated, the battery would last about 0.6 hour for a flooded acid battery
That is if the battery is less than 6 months old, and if the temp is between 0 and 85ºF…

Wil last a lot longer if it is AGM and even more if GEL type, for the same Ah rating
Having said that, when you start, the battery voltage is more than 12, so the current may be less

As the battery depletes towards 10.5V, the current will increase (to keep the Watts constant) and the wire voltage drop will increase (700/10.5= 66.6 Amps)
The algebraic sum of all these factors is quite complex

I hope I am not depressing you too much
Best regards

On August 4, 2016 at 2:03pm
Khalid M. Almagrabi wrote:

I am using regular car batteries (calcium) for solar power bank.

my question is :
What is is the optimal voltage as min / max points that will help to elongate their life.

my solar controller will shut off charging batteries then their voltage reaches 14.5 V in order not to over charge them, but I want to know that is the minimum in order not to under deplete them.

On August 4, 2016 at 4:03pm
Anita wrote:

Only a field trail can answer some of these questions. Your questions are far beyond the scope of a forum like this
2) How long will the inverter supply output? Quick answer is, about 30 to 45 minutes

To charge the battery you need at least 13.6V preferably 13.8V and once in a while (twice a year 14.4V for 1 to 2 hours) when the batteries is/are new, more often when older
If we refer to BU-403 article, it states 12 to 16 hours charging time.
That translates to 185Ah/12h= 15 Amps and 11 Amps charging rate
So the charger output current should be limited to these values to prolong the battery life
One has to understand, every time we charge/discharge the battery we rob some of its useful life
How much? It depends on the chemistry and how deep the discharge.
Generally at 10.5V the wear (or damage) is considered severe!

Regarding the charger’s efficiency (in terms of electrical voltage/current conversion) it depends where the prime energy comes from and a bunch of other factors

2) How long will the inverter supply output? Quick answer, about 30 to 45 minutes

The battery rating 185Ah means the battery will supply 9 Amps and a bit for 20 hours
Ah rating is always based on 20hours

If you plan to use 58A as calculated, the battery would last about 0.6 hour for a flooded acid battery
That is if the battery is less than 6 months old, and if the temp is between 0 and 85ºF…

Wil last much longer if it is AGM type and even more if GEL type, for the same Ah rating
Having said that, when you start, the battery voltage is more than 12, so the current may be less
As the battery depletes towards 10.5V, the current will increase (to keep the Watts constant) and the “wire voltage drop” will increase due to the increased current demand (700/10.5= 66.6 Amps)
Which will result in a sooner 10.5V than anticipated. The wire (copper) has a positive temperature slope
It means the losses will increase with a rise in wire temperature, leading to more loss and more heat…
…thermal runaway. This is the basis how a fuse works.
As you can see the algebraic sum of all these factors is quite complex

I hope I am not depressing you too much
Best regards

On August 10, 2016 at 6:06pm
Anita wrote:

To Khalid M. Almagrabi
What is the optimal voltage as min / max points that will help to elongate their life

you have to read all the stuff at battery university
14.5V is quite high (OK if ambiant is about -20ºC)
at 25º, 13.6V (longer life) to 13.8V (more power less life cycles)
min voltage!
every time you use (charge/discharge) the batteries, you wear them some
at 10.5, the damage is considered severe
it is not recommended do discharge below 10.5V
at that voltage there is not much energy left anyway


On August 20, 2016 at 8:29am
AK47 wrote:

Can we use (discharge) a lead acid battery while charging it by connecting it with some load like table lamp?

On August 24, 2016 at 4:10pm
Anita wrote:

To AK47
yes of course
however to discharge the battery, the charger must either be disconnected or of a lesser value than the load

otherwise the charger will supply the load

On August 27, 2016 at 12:22am
Muhammad Junaid Akmal khan wrote:

Dear Sir,

Hope you are doing well.

We need a professional battery analyzer/tester to analyze Sealed Lead Acid Valve regulated batteries of different brands like YUASA, EXIDE, CSB etc.
Please suggest us some renowned brands of battery analyzers in this regard.
Please send us the maximum information about two or three different types of analyzer which you are going to suggest us along with the availability and Price.
Tester must be compatible to analyze the batteries of 6Volts and 12 Volts with different ampere ratings like 4.5 to 200Ah.

On August 29, 2016 at 12:40am
Andre Van den Wyngaert wrote:

AK47, I’d like to add this: like Anita says, it depends on the current that the lamp consumes and the current that the charger can deliver.
If your charger can supply more current than the lamp consumes, it will power the lamp and in the mean time keep on charging the battery. But your lamp will get the charge voltage, which is higher than 12V; more like 13.5…14V. If your lamp can handle that, there is no problem. It will shine brighter grin
When your charger can deliver less current than your lamp consumes, it will deliver its max current to the lamp, and the battery will also deliver some current to the lamp.

The water analogy might make this clearer: a T-piece connects 3 pipes. Water that flows in, flows out. If it flows in through 2 pipes, it comes out at the third. When it flows in at 1 pipe, if flows out at both others.
The flow is the current.
The water pressure is the voltage.
Highest pressure (voltage) wins and pushes water (current) to the others.

On August 29, 2016 at 5:58pm
Bob Kondner wrote:

AK47: Consider using simple diodes as switches. With both your input power and battery driving through “ORing” diodes you can run you light without draining during charging.

Now this assumes you have access to power from the charger before it hits the charger current limit functions. But you can play a lot of games switching power circuits with simple diodes, and of course a FET can help!

I use “ORing” diodes in my small circuits. I have schematics up on www.sunduino.com. Most of these products are for smaller instrument operation but the overall architecture will work at higher power.

Bob K.

On August 30, 2016 at 4:46pm
Anita wrote:

to Muhammad Junaid Akmal khan

the Cadex C8000 seems able to provide the testing you are looking for.
check-it at


On September 7, 2016 at 7:51am
sulabh wrote:

can I get the chemical equation

On September 13, 2016 at 1:11am
Matt wrote:

Hello. Very nice write-up, thank you. I’m currently dealing with a BTX 12-134 battery and I am considering the charging options. The datasheet suggests a charge current of 0.25xCA for the stage 1, constant current charging stage. That’s 34 A and doing things at such high currents has lots of implications that I wish to get around, if possible. I am therefore wondering about disadvantages of charging at much lower currents (e.g. 5 A). Obviously this will dramatically increase the time spent in stage 1, but will it harm the battery? Regards and thank you—Matt

On September 16, 2016 at 10:31am
Les wrote:

Lets understand AH. The capacity of the battery is is listed in AH, but capacity, known a C is relative to the discharge rate. The faster you discharge a battery the lower it’s C. It is important to understand the at which discharge rate the AH capacity is based on. So it you buy a 9AH battery and the capacity is based on the C8 value then if you load it at 1.125A it should give you 8 hours of discharge current. But if you loaded it a 4.5A (4 times) discharge rate you will not get 2 hours of run time, actually you will be lucky to get one hour.
Most batteries should be charged no faster than around C/4 where typically C is based on the C8 to C20 capacity so charge a 9AH battery at 2.25A and it will last but make sure you have the right type of battery for your application.
A standby battery does not like to be discharged and will reach end of life quickly if discharged more than once in a blue moon. Cycle batteries can handle discharges and give the expected life. Remember discharging to a 20% (DOD) Depth Of Discharge will have a much longer life than a cycle battery taken to an 80% DOD.

On September 16, 2016 at 1:07pm
Matt wrote:

Les, thanks for your response but I don’t think it addressed my question. The question was if there would be any harm in charging the battery with particularly low currents. Not high currents, but low currents. When you say “most batteries should be charged no faster than around C/4”, does that imply that there is no lower bound? So if I felt like charging stage 1 at 10 mA (exaggerating) and wait for ages, that would be just fine?

On September 16, 2016 at 11:28pm
Conundrum wrote:

Interesting fault here, “bad” battery which shows abnormally low voltage (ie 11.14V) but if the battery is tilted +/- 45 degrees 20 seconds later it recovers back to 11.32V
Any ideas?  The charger shoots up to >14V and less than 1A drawn.

On September 19, 2016 at 12:41am
Andre Van den Wyngaert wrote:

to Matt:
in my opinion, it won’t do any harm to charge with a lower than max current. It will just take more time to reach a full charge. And a full charge must be reached every now and then to avoid sulfation. See article http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

On September 20, 2016 at 7:28am
Joe Elliott wrote:

Matt—The answer to your question is that no, there’s no harm in charging the battery with particularly low currents, but now you’ll presumably be faced with my earlier question (largely unanswered from my 06/06/2016 comment above) of how to calculate what the fully-charged charging voltage will be (i.e. when to shut off the charger) when charging with substantially lower-than-typical currents.  (I’ve been researching/thinking about this for years, and so far the best input I’ve received is Anita’s suggestion to terminate charging based on temperature rise, but I’ve also found an old book [specifically this figure https://books.google.com/books?id=mcL3P6x7xTcC&pg=SA3-PA18&img=1&zoom=3&hl=en&sig=ACfU3U27by3zVPY9tyeq-LuYP0KsPhqrPQ&ci=131,116,704,587&edge=0 ] which also provides a clue, but my charging rates are so low that I end up in the truncated part of the curve [and, as with Anita’s suggestion, I’ll still need to make accurate temperature measurements before that chart from the book does me any good].)

On September 23, 2016 at 7:18pm
Anita wrote:

to Conundrum

I have seen similar behaviour but at plateau current
that is when the battery is fully charged and the current wont go down any further
that when the battery is tilted, the plateau current increases sometimes 4 times
(from 100 to 400 mA)
and no change on some batteries. I tend to believe it is caused by stratification

I tried mixing the electrolyte by pumping with the hydrometer, but no success
I am tempted to empty the electrolyte in a container, mix-it, filter-it and put it back in the battery

let me know if you find something

On September 24, 2016 at 2:05pm
Anita wrote:

To Matt

the lower limit has to be above the self discharge of the battery
generally speaking, a system should operate between 10 and 90% of its limits
usually when operation below 1% and above 99% there are some undesirable effects
that takes place
self discharge is one example.

On September 27, 2016 at 11:22pm
nitin wrote:

my device took 2.5A current at 12v, my question is what if i transfer my device from 12v to 5v. what would be my current ?

On September 29, 2016 at 12:50am
Andre Van den Wyngaert wrote:

to nitin:
that is not much information, but I assume that you mean that your intention is to keep your power consumption constant, so you will change your circuit. That is the case when you use e.g. a switchmode power supply.  Power P (watts)= voltage V (volts) x current I (amps).
12V x 2.5A=30 Watts.
30 Watts / 5V = 6 amps.
So at 5V, your device will draw 6 amps to deliver the same 30 Watts.

The story is different if you mean that you have e.g. a resistive load that you will connect to a lower voltage now. Then it will draw less current, according to ohm’s law: Voltage = current x resistance. Resistance is a constant in that case, so if your voltage is lower, your current will be lower and the load will get less power, since power = voltage x current. If it is a 12V light bulb, it will give a lot less light when fed with 5V.

On September 29, 2016 at 2:59pm
Anita wrote:

So Nitin
what is the device?

is it a resistive device?
a constant current device?
or a constant power device as Andre Van den explained

you may want to read about Ohms law

On October 3, 2016 at 3:35am
Philip Joseph wrote:

If i were to connect a Xbox One S to a UPS of 700VA, 230V,
How long would I have before the Console goes off?

On October 3, 2016 at 9:30pm
Samuel wrote:

Good day,

I need to buy a mppt charge controller but I’m struggling to know which module I should buy in terms of the output current. I am using a 50W solar panel and I need to charge a 12V 66ah battery

On October 5, 2016 at 1:16pm
Anita wrote:

To Samuel
It is strongly recommended to consult your vendor
12V 66Ah, what type of batteries?
Usually batteries charge at 1/10 their C (Ah) value
and at what voltage to stop depends on the battery itself

If you decide to connect your panel to the batteries
You need to watch that the voltage does not exceed the battery voltage
some are 13.6V some are up to 15V
Your battery vendor should tell you how to charge his batteries

On October 5, 2016 at 1:24pm
Anita wrote:

To Philip Joseph
cant answer your question, too many variables

but the answer is somewhere between a few minutes and several minutes
the best is for you to try-it out

Best Regards

On October 6, 2016 at 12:31am
Andre Van den Wyngaert wrote:

to Philip Joseph: I found these figures on the internet about your Xbox S compared with an older Xbox version: When watching TV, it’s ~30 watts, which is down from ~78 watts. When gaming, it’s ~50 watts which is down from ~110 watts. In instant-on standby, it’s ~10 watts which the same as the original. In instant-on standby while downloading, it’s ~20 watts, which is the same as the original too.
Assume you are gaming and consuming 50 watts.
Your supply can deliver 700VA. This is max load; it says nothing about how long it can deliver that. So like Anita said, more information is needed.
But assuming it is a small UPS, let’s assume it can deliver 700VA for 5 minutes. VA is not equal to Watts; that depends on the load. An Xbox is far from ideal load, so let’s say you can deliver 400 watts for 5 minutes. Theoretically that would mean you can deliver 50 watts for 5 x (400/50) = 40 minutes.
But to get a reliable real value: indeed, trying is the only option…

On October 14, 2016 at 10:10pm
V.R.SARAPH wrote:

We are interested to know the following about MF Auto Battery
1) About in AUTO-VRLA battery two types one in gel type other in liquid type both Sealed
  and VRLA type mean Container,separators & other components are same expect
2) Or Iin MF sealed liquid type Containers are of open type plug

  3) We are interested to set up project of Auto-MF in liquid type only in India or South
4) Let us know the availability of sch type containers of all ranges

5) We are a team -Engaged in Battery line

  Let us have ur confirmation at the earliest Matter most urgent.


On October 19, 2016 at 11:50am
David S Reynolds wrote:

For Solar storage backup ...

is there an advantage for using 3 pcs of 12v 35ah batteries over a single 12v 100ah ?

On October 19, 2016 at 5:10pm
Anita wrote:

to David S Reynolds
your question is a mater of personal choice/opinion
technically, it is about the same. a bit more for the 3X batteries
The 3 battery option is very likely to have less internal resistance
meaning, it will suffer less in high power demand

However, in my set-up I use the 3-4 battery option because it is lighter to handle!
as oppose to one big battery and break my back

On October 28, 2016 at 4:04pm
Anita wrote:

To Philip Joseph Re October 3, 2016 at 3:35am
did you run your system to find-out?
there seems to be several varieties of Xbox
I have a power supply here that is 12V 16.5A output (over 200W)

since it is 12V to start with, I would connect-it directly to the UPS battery
to avoid converting to high voltage DC then to AC (in the UPS), then 120VAC back to 12V DC in the Xbox power supply
If your system is 12V it will be far more efficient to run from the 12V battery

let us know how it went
Best Regards

On November 14, 2016 at 2:55pm
Joe Elliott wrote:

New question: Two nights ago my charger automation failed, and the charger continued to charge the batteries for ~8 hr longer than it probably should have—current was just under 0.01*C when the issue was discovered and the charger unplugged.  Now the question is whether damage may have been done to the batteries.  This is a converted EV application that has both flooded and AGM batteries in parallel; starting with the flooded ones (the AGM pack is harder to access to inspection purposes), I opened the electrolyte caps, expecting to see a lack of electrolyte (from boiling), but instead I saw electrolyte levels consistently ~0.1” higher than they had been previously!  Can anyone tell me if this is this somehow normal (how?), or if it’s symptomatic of having damaged the plates of the batteries, or some other phenomenon?  Thanks.

On November 20, 2016 at 8:14am
Keith Brescia wrote:

I just finished giving my Sears DieHard deep cycle marine battery a full charge with a new Sears automatic charger that stopped charging in what appeared to be normal operation, showing a green light to indicate full charge.  After standing overnight the voltage is 12.6 with no load, about right for upwards of 90% charge, but the specific gravity is only about 1.175, as compared with 1.250 specified for 90% charge.  My reading is what it should be at about 40% charge.  The hydrometer checks out OK with concentrated salt water in that range.  The battery is about 4 months old and has had a couple of deep discharges, the second of which was about 60 AH in a torture test of 24A for 2.5 hours, and pulled the battery down to under 8V under load.  It recovered to over 11V no load after standing few minutes.  I am now testing the battery with a 1A load to see how many AH it can deliver over the next two or three days.

Does that low specific gravity suggest that my torture test may have damaged the battery?

On November 21, 2016 at 4:07pm
Bob Kondner wrote:

  From what I have read some vendors use a acid density under 1.25 to reduce corrosion, I do not know if that is true or not. I have some Rolls S-460 and the 100% point is specified at 1.265. The only way I get close to that is using a very low charge (like 1 amp) for a long time. I then see the density rise in that case. Getting a battery to more than 90% is difficult. The manufacturers are, I believe, in a specs war and they pull every string to get the numbers high. So yes my Rolls S-460 are rated at 350AHr (20Hr Rate) but at 100 hours it is 461 AH.

Think of charging the same way, it takes 100 hours plus to fully charge, few if any chargers will do that. It also depends on how hard (as in how many volts) you want to use during charging. Higher voltages help complete the charging process faster but it also generates gas. I don’t drive hard or long and I am happy to get 275AH. These units have not required water in 4 years. I am guessing ( IE hope) that my gentle use prolongs life.

I doubt you damaged thing with a heavy load on just 1 or 2 cycles. Also in some small 12 lead acid AGMs I have see it take a number of cycle to show a full capacity.

I would suggest not worrying about the 90%. If you really need another 10% add a battery in parallel.

Bob K

On November 22, 2016 at 7:29pm
Keith Brescia wrote:

Thanks, Bob, for your response.  I got about 50AH out of the battery with a 4.5 ampere test load, to simulate running my telescope accessories overnight.  That seems like a reasonable capacity for the size of the battery, which is about the size of a car battery for small or midsize cars.  Sears does not give the courtesy of a published ampere hour capacity.  All they give is cold cranking amps, which seems out of place here as this battery is designed for deep discharge cycles while running a small trolling motor, not for optimum bursts for starting a car.  The battery kept a 1.3 amp load going for about 40 hours total during four nights at a remote camp site.

Now that I think about it, maxing out the chemistry of the plates could leave the density lower if this particular battery has a larger volume of acid than does a typical car battery.  To go to extremes, imagine putting the same plates in a huge vat of acid.  There is a limited amount of lead to be charged or discharged, so I would expect less change in density if we have an excess of acid.  Can any chemist help me with this line of thought?

On November 23, 2016 at 10:41am
Bob Kondner wrote:

Hi Again,

I am not a chemist but if you have a “Car Sized Battery” I would guess it is 100AH? Is that correct? Got a model numbers?

For a 40 hours discharge at 1.3A you only got about 52 AH, that does not jive with the 50AH you got at the 4.5 A discharge rate! I suspect you are far from charging that battery to full.

Suggestion: Put it on the Sears charger, let it charge. Then take a lab supply and charge it at 1 amp. Watch the SG of the acid. (This must be a flooded plat battery, (Hmmm I would thing a true deep discharge would be AGM?)

If you charge at the 1Amp level for a while you should get full capacity and you should see the SP rise to the expected level. I suspect your Sears charger is not charging a deep cycle properly. Got a model number for that sears charger?


On November 24, 2016 at 8:47am
Keith Brescia wrote:

Bob, thanks again for your tips.  I think I have enough stuff on hand to improvise a charger that can be forced to higher charging voltage and then be operated manually to deliver the charging sequences described in this article.  I would monitor it carefully with the battery under an exhaust fan hood, and needless to say I would have acid splash protection on.  It is a flooded battery, and I have distilled water I can add should my actions cause water loss from excess gassing.

I charged the battery with an old charger before the camping trip over Labor Day weekend, but I did not check the level or the voltage under load before or afterward.  I may or may not have been anywhere near a full discharge. I found this article just last week and then got the new charger and a hydrometer.

On November 25, 2016 at 6:58am
savio dsouza wrote:

Folks, I have a 30 W solar panel with Voltage 17.5 current at 1.75A. I will insert a 6A , 12V PWM charge controller to charge lead acid battery. My question is what ,max capacity battery can I change with this solar panel. I have a 120AH Lead Acid battery with me. I have not connected these 3 yet as I am awaiting delivery of solar charge controller.

On November 25, 2016 at 11:29am
Bob Kondner wrote:

You can charge any size battery you wish.

On November 25, 2016 at 2:49pm
Keith Brescia wrote:

Battery:  Sears DieHard #50124 Size JC-24CM (24M)
          550 CCA, 140 minute reserve capacity, whatever that means.

Charger:  Plus Start #71228, bought at Sears.

Yesterday I charged all day, until the Plus Start charger was down to less than 0.5 amp.  Indicated voltage about 14.0 volt, specific gravity about 1.175.  The charger would have quit within another hour.  I then modified my 40-year-old charger, bypassing the voltage regulator and plugging it into a Variac to manually set the voltage.  I have been giving the battery a steady 1 ampere the past 20 hours, and the specific gravity is now between 1.210 and 1.225.  The external volt meter, also very old, is showing 14.8 volts.  I am going to let it run a while longer and try to get the specific gravity up to 1.250, and then do another run time test at 5 amps or so.  My hunch now is that the automatic charger function is maladjusted and that my old volt meter is reading high.  Perhaps I should spend some more money for a good charger specifically designed for deep cycle marine batteries.

On November 25, 2016 at 3:43pm
Bob Kondner wrote:

  As for your battery with a Reserve Rating you really have no serious specs to go on. Once you get the SG to where it should be (by monitoring manual charging) you can then measure the capacity you get with your load current.

The 14.8V is probably a good value, I would expect that. You need to drive to higher volts to push in the last remaining capacity.

As for the charger it has almost zero specs about how it works. If the 6 amp setting completely terminates the charging then try the 2A which they call a trickle. You may need to add your own timer to limit charging. But make certain the charger does not discharge the battery once it is turned off.

You have discovered how much logic is not provided in low cost chargers. And even with move expensive chargers you do not have access to all parameters. But 99% of folks are not concerned with the last 10%. Be real happy if you find a commercial charger that gets you to 90%.

Bob K.

On November 25, 2016 at 8:40pm
Keith Brescia wrote:

About 8 hours since last post, specific gravity up to 1.235 average, only about .005 spread across all cells.  This is a virtually linear progression since I started this constant 1 amp charge last night.  I am going to let it run overnight at this rate and check it first thing in the morning.  According to chapter BU-903, fully charged deep cycle battery can be 1.300 or more.  This is reinforcing my idea about a wimpy charger and a defective voltmeter.

On November 27, 2016 at 8:15pm
Keith Brescia wrote:

I kept up the manual 1 amp charging until the SG reached 1.250, which is typically about 90% charged.  Then I ran a 4.6 amp load until the SG got down to 1.100, a bit lower than I intended.  That was 15.5 hours, which is about 70 AH.  Clearly the battery is in much better shape than I originally thought, and simply was undercharged by a mismatched charger.  It is now on the Plus Start charger for an overnight run, and I will follow up with the manual charger as needed.

On November 29, 2016 at 8:38am
Bob Kondner wrote:

Great, You are getting good reasonable capacity. How did you set that 4.6A load? was it a fixed current or just a resistive load? If you look at various spec sheets you will find they typically discharge really deep. Probably not something good, discharge deep and life drops like a rock, at least that is what I read.


On November 30, 2016 at 11:40am
Parth Sharma wrote:

i am doing CCCV charging for a lithium metal oxide cell. the max voltage is 4.1V, when the battery voltages reaches 4.1, the supply switches to CV mode but the current drops to 0 immediately and not gradually.
anyone knows what i might be doing wrong?
Thanks & regards,

On November 30, 2016 at 5:14pm
Bob Kondner wrote:

It could be a problem with a protection board causing the series FETs in the pack to open.

On December 1, 2016 at 4:17am
Pramod Trivedi wrote:

A loco engine used batteries 3 x 8 v / 450 ah were put on charging at about 30 Amp. charging current, but 2 nos batteries busted after 3 hrs of period of charging.
What may be the reasons of busting of batteries.

On December 3, 2016 at 8:43pm
Keith Brescia wrote:

After a couple of discharge-charge cycles I have estimated a nominal capacity of 75 AH for my battery.  In delivering 60AH into a test load, the drop in SG showed about an 80% discharge.  I compared the size and weight of this battery with those of a 90AH battery advertised online and these numbers were in good agreement.  For measuring discharge I used a simple nichrome wire resistive load and monitored it with an ammeter.  The voltage and current dropped during the run, so some rough and dirty calculus got the total discharge figures.

The Plus Start charger delivers a steady 5 or 6 amps in a bulk phase until the voltage reaches 14.0, at which time it starts tapering off in what should be the acceptance phase to complete the charge.  That works fine on the built-in 25AH battery in my DieHard 1150 portable power pack, but when it did this sequence on the deep cycle battery the SG indicated well under 50% charge.  With the improvised manual charger I went from there with 4 amps, the most it can manage without overheating the Variac, until the SG got up to the 75% mark, and then manually tapered off while checking the SG frequently.  The voltage during this acceptance phase was about 15 volts, which was too high according to some sources but was described as OK by others.  With these conflicting opinions I cannot tell whether this battery has excessive internal resistance as a result of neglect or if it is normal.  If the former, how is any automatic charger going to adjust to it?  I am in a quandary about whether to buy an expensive charger or to make do with my manual setup.

On December 4, 2016 at 8:16am
Keith Brescia wrote:

I just did a momentary load test on the big battery.  The voltage across the terminals dropped only about 0.1V with a 5A load.  That suggests that there is not enough internal resistance to fool a properly programmed automatic charger into quitting when the battery is less than 50% charged.  This brings me back to this other source where the author says that 15V is a normal acceptance phase voltage for a deep cycle battery.
If they are right, it is simply that my cheap Plus Start charger, while satisfactory for a car battery, is not so for a deep cycle battery

On December 5, 2016 at 4:34am
ankit wrote:

can i charge 35ah,12v amaron battery from exide 150ah,12v battery by parrallel connection.
please answer in yes or no. and why ?

On December 5, 2016 at 4:04pm
Keith Brescia wrote:


That would depend on whether or not the two batteries reach acceptance phase at the same voltage.  If they are mismatched as my batteries appear to be, getting to a full charge of the one that requires higher voltage will overcharge the other one.

On December 5, 2016 at 4:34pm
Bob Kondner wrote:

  Look around the web for multi phase chargers and you will find many variations.  You can look at my www.sunduino.com site where I have small battery chargers though I have played with larger lead acid, flooded and AGM. You almost need a charger with 4 phases where the user can adjust the setting for phases and their transitions. But that would be WAY to complicated for 99% of the users.

I think your last statement about the charger not being really good for your deep cycle battery is correct. And a deep cycle is different from a starting battery so I am not surprised. Check out some multi phase chargers (Bulk, Taper and Trickle ) but be prepared to spend more. And don’t go for a lot of charging amps, all that does is bump you out of bulk early. And trickle charging without a timeout is not good for a battery. Give it 24 or 48 hours if you want the last few percent of capacity.



On December 5, 2016 at 7:01pm
Keith Brescia wrote:


Please disregard my first answer, as I think I misunderstood you.  If the big battery is fully charged, it will partially recharge the small one.

On December 5, 2016 at 7:14pm
Keith Brescia wrote:

Addendum to my battery and charger testing:  I stopped my topping-up charging of the deep cycle battery when the SG reached about 1.270.  After letting it stand for 24 hours the SG was up to 1.300, which some sources say is good for a deep cycle battery.  Today I did a 48AH discharge over about 11 hours and an immediate SG reading was about 1.185, and I will check it again sometime tomorrow to see where it stabilizes.  I will follow that with more charging tests.  In the meantime I know someone who has a modern electronic multimeter and I compare my old voltmeters with it.

On December 7, 2016 at 6:40am
Keith Brescia wrote:

After letting the battery stand overnight I checked the SG Tuesday morning and it was unchanged at 1.185.  I then let it charge all day with the Plus Start charger.  The charging current held at 5.5A for several hours until the voltage reached 14.4V, and then started tapering off while the voltage held.  The SG at that point was 1.200, which was well under the nominal 75% charge level specified for starting the acceptance phase, but by this morning it was up to 1.250, nominally 90%.  The voltage this morning was about 13.4, right where it should be for the float charge.  I am starting to think the charger is doing a satisfactory job with this battery, and that my immediate SG readings during the process were low because of stratification that clears up upon standing with a trickle charge.  It makes perfect sense that the dense acid that forms between the plates would trickle down initially, and even if it didn’t, it would be slow in diffusing up to the surface layer I can reach with the hydrometer.  Now I am forcing 1A manually for an hour, which I don’t think will hurt the battery, and I will then watch the SG for 24 hours on float charge to see what happens.  At this point I am glad I did not jump the gun and order an expensive charger that may or may not be any “smarter” than the one I am using now.

On December 8, 2016 at 7:11am
Keith Brescia wrote:

Now I am thinking I may have misread the hydrometer the first thing yesterday morning.  After a couple of hours of trickle charge it was 1.230.  After a few hours of about 1/2 amp and then letting it stand overnight on float charge with the Plus Start charger it is up to 1.250.  As in a previous cycle I can forcibly charge it manually and the SG rises at a rate consistent with the current for a battery of this size, but by the book it is requiring excessive voltage, on the order of 15V.  Nevertheless the battery is giving good run time on a test load.  I remain as uncertain as ever about just what is happening here.

On December 8, 2016 at 3:12pm
Bob Kondner wrote:

I assume that during charging you have some gas forming, I would think even a small amount of gassing would stir up the acid. I played with this long ago by using the hydrometer rubber bulb to stir up the acid after charging, I did not see any affect of this manual stir.  The 15 volts does not surprise me. Chargers I have seen always spec the 14.8 - 15.0+ as the maximum for a multiphase bulk charge. I would be curious as to any other specs.

I would suggest you get a copy of “Batter Reference Book”  by T R Crompton. You will find references to 2.65+ V / cell (almos16V for a 6 cell 12volt battery). There are different constructions of batteries and various temperature affects. You probably want to charge at a low current (1/2 amp) for a long time watching the SG and voltage. Full charge is defined with the SG and battery voltage stop going up.

On December 14, 2016 at 2:26pm
Keith Brescia wrote:

Bob Kondner, thanks again for your input.  I did another run test that ran the battery down to about 50% charge.  Then I used the Plus Start charger until it quit.  The SG at that point seemed too low for the known number of AH the charger had delivered, but it rapidly came up when I forced enough acceptance phase charging current to induce bubbling, and then continued to rise at a rate that looked right as this charging continued.  At this point I was watching the voltmeter and reducing the current manually.  I quit Monday evening when the indicated SG reached 1.270, but right now I am resuming it at 0.5A.  Since this battery has been as high as 1.300, I will push it a while longer.  I just found a PDF of Crompton’s book online, which I will consult.  With this, along with your remarks and other sources I have found online, I would conclude that the tight voltage constraints specified above on this page are not to be taken as gospel.  I am retired and as such I can pick times to charge manually and keep an eye on the voltage and current, rather than spend a lot of money for a “smart” charger that may or may not deliver the goods with this particular battery.

On December 15, 2016 at 11:44am
Devon wrote:

I have a 36 volt floor scrubber/sweeper that has a qty of 6 6 volt 360 amp hr batteries. What size charger would I need to fully charge these batteries. The ones in the unit now are a little over a year old. When they were first installed the unit could be used almost all day (8 hrs shift) with out having to recharge. Now it will last about half that time. When the batteries are fully charged they have 37.89 volts which comes to 2.105 volts per cell.

On December 20, 2016 at 11:33pm
bilal wrote:

Sir i have a battry 7.2 v how many voltage charger sport for this bettry

On December 22, 2016 at 7:07pm
Gene M wrote:

HI, I’ve been referencing this site for a while and really appreciate the amount of effort it requires to maintain as new info becomes available.
I do have a question: I have a small motorhome that has two 12v AGM batteries in parallel on a smart charger. I want to use the batteries for short “off the grid” camping stints. I have a voltage monitor and would like to know how low I should allow the voltage to get before cranking up the generator. I see a lot of different opinions and am just not sure if I should discharge to 50% or 80%.

Also is there a handy calculator available that would be helpful with different loads and time durations?

Any advice will be taken into consideration. Thanks in advance.

On December 26, 2016 at 10:49am
Bob Kondner wrote:


I have played with this concept as an emergency power system for home.  Major Params:

1. Size of batteries.
2. Load the motorhome, both continuous and burst . (For example motor starting of a refrigerator.)
3. Size of generator.

I figure you want to use a very quiet gasoline powered generator. The small quiet units are typical about 1K watt. Some larger are 2KW. (Honda and similar)

The major inconvenience is getting out the generator and starting it up. A larger battery/ small load helps here. The other issue is gasoline consumption. A tiny generator that runs full throttle can provide power for a charger and your DC to AC converter for a long period with less gasoline. The ECO system on small generators are not sufficiently fast to handle motor start transient, the generator output shuts down as the generator spins up. Together they need to work like a “Hybrid Vehicle” power system or as a UPS. You must be careful to use a DC to AC converter that will supply the peak power plus average draw. And I found a sine wave output invert is required for many loads. (Motors as in a refrigerator or the air blower in my gas furnace.)

So my suggestion is get a tiny generator to drive your charger and run it as often as possible. Less wear on the battery system. If the load is lite and battery fairly large then let it run down to 70% or so then use the generator. Just watch out for peak loads, a partially discharged battery can have problems with peak currents.

Also, If possible, wire the two batteries in series for 24 volts. Higher voltages mean less amps and this is much easier on cables. Next time I will move to smaller batteries but more in series, for 48V.

Bob K.

On December 29, 2016 at 7:18pm
Gene M wrote:

Hi Bob, I believe you are responding to my post, maybe not as I have not read all post’s earlier than mine.

If this is the case, then Thank you for the response.

My MH has a 4kW generator that will charge the batteries and we have done some dry camping on one coach battery. I just installed a second to bring my total power up to 184 amp hours. The two batteries are the same size and type (AGM, group 49).

The question I am trying to get answered is “how low I should allow the voltage to get before cranking up the generator. I see a lot of different opinions and am just not sure if I should discharge to 50% or 80%.”

Any idea?

On December 29, 2016 at 11:57pm
Abishek wrote:

if my Battery gone to low 6.5 V DC(12 V/150AH).,How can i recharge again.. since my Inverter not make it charge..since it is saying as battery voltage too low.. But i heard from battery service engineer it can be charge while another 12 V battery takes in parallel… That means if i connect another battery 12V, total battery voltage will be 9V.. is it ok for charging the same..

On January 1, 2017 at 5:09pm
Bob Kondner wrote:

  50% sounds very low. A lot depends on temp. I can also see times where a motor starts, the battery voltage drops and almost instantly the inverter shuts down. Real Bad.

Measuring your peak currents is a difficult measurement to make. And then knowing how your battery voltage will drop (don’t forget temperature) is also hard to figure. And the final number you get will vary wildly with state of charge and temp.

So best I can suggest is play with it over time. There are just to many variable to do much design. I hate to guess at stuff but I don’t know what to suggest.

What I have done is take a large load and a battery you know is at say 75%. Apply a load for 5 seconds, watch the battery voltage. When you get to a load that brings down the battery voltage to where your system fails you know your current limit. Compare that test load to your peak load and you know if your battery is too small.

It is a big compromise.

Bob K.

On January 3, 2017 at 9:32am
Gene M wrote:

Hi, Bob thanks for the response.
I do not use an inverter, what I’m trying to do is just use my straight 12vdc for periods of time and then run the generator to recharge, unless we get back on the road. So, I guess I will have to experiment to find the length of time my batteries will last to a given charge percentage based on the output voltage of the battery set.
Do you have any experience running AGM batteries, and if so is 60% a safe charge level to bring them down to before charging or is there a percentage I should use instead?

On January 3, 2017 at 11:43am
Salee wrote:


I have just started picking up some knowledge about lead acid batteries and there is something I cannot understand.

Every single article about charging lead acid batteries explains the critical C-rate, which should be gently kept within 0.1C and 0.3C depending of the exact type of the lead acid battery, and charging can take up something around 10 hours, or even more for the big guys. And of course after the topping charge, further charging should be reducet to float charge levels.

However if I think of a poor car battery, that is ment to kept in conditions far away from this, having to suffer from very tough conditions. The car alternator does not used to be that soft, even my small gasoline car has a 70 Amps rated generator, which may pump 30-40 Amps (or even more) into the battery, after the start. This is almost 1C. Moreover the voltage regulator never switches to floating voltage, it is ment to keep it around 14,4V.

In cars charging rate is extremely fast. A cold, “very slow cranking” (guessing the voltage around 11V) morning after a 10 minutes driving the battery is well charged, spins the cranking like a turbine. My last battery worked for 5 years during these conditions.

Well, of course I see the point, starter batteries are designed to live with these conditions, but it is not the same I can read about lead acid batteries.

On January 3, 2017 at 12:15pm
Bob Kondner wrote:


Ok, so you run from DC.

AGM, yes I have played with a deep cycle 100AH batter in some detail. Going down to 60% is still a lot if the temp is low. Still depends on peak currents and the voltage required at those peaks.  At 12V I suspect you have fairly long wires (long is greater than 3 foot) to your loads. I assumed you have an invert and like min very close to the battery (< 2 foot). Pulling 2KW is 200 amps and wire drop plus battery drop will drop out the inverter quickly. With your

On January 3, 2017 at 3:11pm
Bob Kondner wrote:

Slow cranking is more like 8V.  If you check around you will find that cranking amps is specified at a very low voltage. After 10 minutes the engine is warm!

With 14.4V fixed voltage charging you probably will not get anything near 70 amps charging.  I would consider that 14.4V more like a “High” trickle. If it was continuous (car always running) yes it would be way to high. Much lower and you would not get much of a fast charge. It is a good compromise for a fixed voltage charger.

On January 3, 2017 at 4:10pm
Gene M wrote:

At this point we’re fair weather (May to October) campers so the temp doesn’t get that low I use 2ga. wire for my feeds, and the only motor is the water pump. I do understand your temperature. My load looks like 11.85amps overnight.

On January 14, 2017 at 4:52pm
anita wrote:

Abishek   December 29, 2016 at 11:57pm
6.5V no load! this is very bad
I would not recommend connecting another battery in parallel, as large currents may flow and cause a fire or explosion

many (most) battery chargers need some voltage to start the charging process. This is to avoid sparks when connecting
maybe you can revive the battery with a lab power supply, set it at 13.8V, with current limit to 1A
depending what happened to the battery, it may take a while (days) to recover

If with a lab power supply limited to 0.1A check how much voltage is needed to conduct 0.1A, if more than 13.8, much more (like 30 or even 60V) then the battery is sulphated

On January 18, 2017 at 5:37am
NabuN wrote:

@ Abishek

I agree Anita and I want to add some ideas, based on my personal long experience
and passion for batteries :
“I would not recommend connecting another battery in parallel, as large currents
may flow and cause a fire or explosion ‘...but you can put an incandescent auto
bulb 12V 21W..50W in series to limit the current that occur at the parallel connection.
After some time (minutes…hours), the charger will start and you can disconnect
the helping battery.
If battery is sulfated, “..maybe you can revive the battery with a lab power supply,
set it at 13.8V, with current limit to 1A “... but if you don’t have lab PSU
you can use a simple rough charger or an available AC adapter of the laptop, any type,
15..24V and two 12V bulbs in series having maximum 10W (the current must be
limited to 1%..5% of battery capacity) and wait one or two weeks to reach results
...the voltage will increase slow to 12..12,5V if battery is not defective.
Then, connect a 3..5 stages charger to complete the charge process.

Good luck ! grin