BU-408: Charging Nickel-metal-hydride

Charging Nickel-metal-hydride

The charge algorithm for NiMH is similar to NiCd with the exception that NiMH is more complex. The NDV method to measure full charge shows only a faint voltage drop, especially when charging at less than 0.5C. A hot battery or one with mismatched cells works against the already minute voltage drop.

The NDV in a NiMH charger must respond to a voltage drop of 5mV per cell. To assure reliable charging, NiMH chargers must include electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. Modern chargers achieve this by combining NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm. These “or-gates” utilize whatever comes first depending on battery condition. Many chargers include a 30-minute topping charge of 0.1C to add a few percentage points of extra charge.

Some advanced chargers apply an initial fast charge of 1C. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. The charge continues at a lower current and applies further current reductions as the charge progresses. This scheme continues until the battery is fully charged. Known asthe “step-differential charge,” this method works well for all nickel-based batteries.

Chargers utilizing the step-differential or other aggressive charge methods achieve a capacity gain of about six percent over a more basic charger, an increase that is not possible without stressful overcharge. Although a higher capacity is desirable, filling the battery to the brim has a negative effect in that it will shorten the overall battery life. Rather than achieving the expected 350 to 400 service cycles, the aggressive charger might exhaust the pack after 300 cycles.

NiMH cannot absorb overcharge well and the trickle charge is set to around 0.05C. In comparison, the older NiCd charger trickle charges at 0.1C, double that rate. Differences in trickle charge and the need for a more sensitive full-charge detection render the original NiCd charger unsuitable for NiMH batteries. A NiMH in a NiCd charger would overheat, but a NiCd in a NiMH charger does well because the lower trickle charge is also sufficient for NiCd.

It is difficult, if not impossible, to slow-charge a NiMH battery. At a C‑rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer. Harmful overcharge will occur if a fixed timer controls the charge. This is especially apparent when charging partially or fully charged batteries.

The same scenario occurs if the battery has lost capacity due to aging and can only hold half the capacity. In essence, this battery has electrically shrunk to half size while the fixed timer is programmed to apply a 100 percent charge without regard for the battery condition. In most cases an overcharge will heat the battery, but this is not always the case. A poorly designed NiMH charger is capable of overcharging a battery without heat buildup. At a sufficiently low charge rate, NiMH can remain totally cool and yet suffer from overcharge.

Battery users are often dissatisfied with shorter than expected service life of a battery. Let’s not blame the battery manufacturer, because the fault might lie in the charger. Low-priced consumer chargers are especially prone to incorrectly charging. If you use such a charger and want to improve battery performance, estimate the battery state-of-charge and capacity and set the charge time accordingly. Remove the batteries when you think they are full. If your charger charges at a high charge rate, do a temperature touch. Lukewarm indicates that the batteries may be full enough for removal. It is far better to remove the batteries and then recharge before use than to leave them in the charger for eventual use.

Note that some nickel-based batteries heat up during charge and this is in part due to high internal resistance. Such a battery may be warm to the touch even though it is only partially charged. Another battery might be fully charged and remain cool. Charging NiCd and NiMH batteries on an inexpensive charger is guesswork, and it is best not to charge them longer than necessary. Remove the batteries when perceived full and give them a quick charge before use.

Simple Guidelines on Charging Nickel-based Batteries

Comments

On May 3, 2011 at 6:50pm
farhan wrote:

please i need information about the white powder released ffrm nickel mh batteries within next 12 hors before 3pm 4th may 2011..please tell me what that powder chemical is and about crystalline or amorphous..

On May 16, 2011 at 12:07pm
JMD wrote:

And this charging page for NiMH tells you everything BUT the charging of NiMH… It only tells you what C-rate you SHOULDNT charge your cells with - not the recommended C-rate.

So.. what is the recommended C-rate for charging NiMH???

On September 9, 2011 at 9:11pm
Edward wrote:

the best C-rate for chargeing NiMH is 0.2C-rate charge 6Hours

On September 10, 2011 at 12:52am
Peter den Hartog wrote:

Dear Isidor,
I have a question regarding household appliances with NiMH batteries. I own a 18V Black and Decker pv1825n Dustbuster. I found the batterypack details here: http://service.blackanddecker.co.uk/Products/ProductPartsBDK.aspx?ProductID=8339
The factory charger is 7.2-24V voltage converter (85mA). Charge time is around 21hours.
The manual recommends leaving the machine connected to the charger when not in use. I am not sure that would be the correct way to improve lifespan. Regularly, I use the machine every two to three day for a few minutes. From what i have learned off your site i guess the following would be better:  charge for 24h, disconnect from charger, use regularly untill I notice capacity starts to drop, charge again for 24h etc.  Additionalym a deep discharge every three to four months is a recommended.
What would be your opinion in the case? I find that a lot of appliances come with batteries and instructions that i cannot match well with the information on your site.
My compliments on an excellent website! It has helped me on many occasions and I have made myself an expert in the eyes of family and friends with battery problems (there are many) just by relaying the information i found here. Many thanks!

On September 13, 2011 at 3:17am
Edward wrote:

I am the battery engineer from one of the leading rechargeable battery company
Firstly ,the charge time is 21hours is not reasonable , it is too long time, when the battery is fully discharged ,you must to wait too long for the sencond discharge
Secondly,When the machine not in use for long time such one day or longer, you’d better disconnenct the charger , it will be better for the battery cyclelife. as you know overcharge will be a waste of electricity and will short the battery use life.
Many household appliances supplier worry about that the user can not fully charge the battery which leading to the short run time and complaint .due to the self-discharge of ni-mh battery, in fact , the self-discharge in a short time such as one day or two days is neglectful, and long time overcharge with trickle will be bad for the battery life

So i agree your method to charge and discharge the battery

welcome to discuss this issue

On October 3, 2011 at 2:52am
Jeffrey wrote:

I work on a government base where rules are strickly followed concerning safety.  My NiMH batteries for my e-bike are in 15 lb packs of sealed f-cells. (by design 24v, run in series)  Do NiMH batteries give off any gasses while charging? What hazzards exist when charging the batteries? (Such as fire, leaking,  (I know that Lead acid batteries do and my boss is wanting to wrap me into the same category, leaving me to prove that the NiMH batteries are safe.  I need manufacturer documentation to prove this, but my batteries are generic. ON a seperate note, if I charge my batteries in a refrigerator to reduce their heat during charging, I notice that they charge faster.  I also notice if I charge them to full then reset the charger after a eight hour full charge that my batteries get an extra 1-3V overall.  (normally I am at 57 and if I reset I get upwards of 59.5 after another hour and a half of charging.)  Am I hurting the batteries using either process?

On October 7, 2011 at 8:30am
Edward wrote:

there is a safety venting in the battery cap, which will open to give off gasses to release the battery inner pressure when the battery is deep over charged,so, do not deep over charge the battery to long time ,it will lead to leaking even fire or explode
the charge efficiency is related to the temperature, the higher temperature the lower charge efficiency , so, you can charge the battery faster in the refrigerator to reduce their heat during charging.  we advise not to reset the charger when the battery is fully charged
to prevent from deep over charged

On December 13, 2011 at 9:49am
Erlen Ruperti wrote:

I work on a R&D institute in Brazil and we’re performing an analisys on NiMH battery for UPS system (aprox. 150W@12V). In this case battery will be constantly charging. Even if I use the proper trickle charge is there a risk of deep over charge?

On December 15, 2011 at 8:09pm
Edward wrote:

If the trickle charge is between 0.03C and 0.05 C, there is little risk of deep over charge , However , If you can control the trickle charge every day for one hour to keep the battery fully charged, that will be very good for the battery life.

On December 22, 2011 at 6:11pm
Jim wrote:

I have a 20mA constant current source charging a 9V 180 mAHr NiMh battery with a microprocessor A/D that measures the terminal voltage.  When the terminal voltage reaches 9.0 software shuts off the charger.  The time to reach 9.0 volts from a pretty much discharged state is about an hour so my hunch is that the battery is no where near fully charged but the terminal voltage really never increases much past that level.  Can the can the state of charge be determined from terminal voltage alone?  I’ve seen tables on flooded lead-acid batteries that relate voltage to percent of charge, but never on NiMh. Is there such a thing?  -

On December 23, 2011 at 11:01pm
Edward wrote:

The Lead-acid battery is different with Ni-mh battery. As we know, For ni-mh battery ,the fully charged voltage will become higher after some cycles. So, the 9V 180 mAHr NiMh battery can be fully charged controled by the 9.0 volts terminal voltage ,and 20mA when the ni-mh battery is new .but, after some cycles the fully charged voltage will be higher than 9.0V.
We can control the charge by many condition, such as /time, -deltV dt/dT /T.max/ Volt. max
and so on
thank you

On December 30, 2011 at 1:08am
sean wrote:

I have “old”  large capacity 12v NiMH modules (100AH) which I need to keep above 9vdc.  I read that trickle charging is not recommended.  What would be the recommended “top-up” rate ?

On January 4, 2012 at 9:39am
VooDude wrote:

The statement that NICd chargers aren’t good for Ni-MH cells does not take into account the four-fold increase in cell capacity that took place over the time period where Cadmium cells were displaced by metal hydride cells. Consumer trickle-chargers for NiCd batteries do not adjust themselves for the capacity of the cell.  The old trickle chargers I had for 600mAH NiCd cells might not be well suited for 600mAH Ni-MH cells, but AA cells in Ni-MH are now 2,000 to 3,000 mAH, so the fast trickle charger that pumped 0.2C/h into a 600mAH NiCd cell is now a slow trickle 0.05C/hr charger, even though the 120mA current flow has not changed.  I still use my 1980s vintage NiCd chargers with good (but not optimum) results - VooDude

On January 8, 2012 at 12:22pm
Harvey wrote:

In everything I’ve read it seems that the worst enemy of Ni-MH is over-charging. My interest is in the long term health of the cell. Would the cell suffer any negative side affects if it was repeatedly charged to only 90% of charge each cycle, maybe by charging at .2C and terminating when deltaT just starts to increase. 
Thanks

On January 8, 2012 at 11:26pm
Edward wrote:

there is no any negative side affects if it was repeatedly charged to only 90% of charge each cycle at 0.2C , But the work time will short a little ,i hope you do not mind that
thank you

On February 29, 2012 at 10:36am
Juan Carlos wrote:

Cuanto tiempo debo cargar una bateria NiMH 7.2 de 1800mAH y cuanto tiempo debe durar la carga de esta bateria. Gracias

On March 6, 2012 at 8:57am
Stu wrote:

Jim wrote:
“I have a 20mA constant current source charging a 9V 180 mAHr NiMh battery with a microprocessor A/D that measures the terminal voltage.  When the terminal voltage reaches 9.0 software shuts off the charger.  The time to reach 9.0 volts from a pretty much discharged state is about an hour so my hunch is that the battery is no where near fully charged but the terminal voltage really never increases much past that level.”

Jim you don’t have a (nominal) 9V NiMH battery, as the nominal voltage will be a multiple of 1.2. So you have a NiMH in the form factor of a 9V (PP3) battery, but the actual nominal voltage will most likely be either 7.2 volts or 8.4 volts.

To determine the correct final voltage it’s important that you know the number of cells (nominal voltage). If it’s not marked on the battery then measure the open circuit voltage of the battery when it’s getting close to (but not quite) discharged, and see if it’s closer to 7.2 or to 8.4.

My 8.4V 180mA (9 volt PP3 replacements) reach a final voltage of around 10 volts at a 0.1C (18mA) charge rate. A final voltage setting of 9V will be too low for an 8.4V nominal NiMH to charge more than about 20% maximum.

Also be aware that the “correct” final voltage will change with temperature as well as with battery age/condition, so it’s best to have a time limit to the charge as well.

On March 12, 2012 at 12:04pm
George wrote:

hi,
NiMH batteries are new for me and I want to find some tips for charging and preserving them,I announce you that I have 4 AA batteries Energizer of 2500 mAh and 4 Sanyo 2700 mAh normal (not LSD) and 4-channel smart charger that charge all batteries fully discharged in 3 hours:
1. keeping the battery empty for a week or longer is damaging it ?
2. if the battery is at 70% of capacity and I begin charging , is this damaging it ?
3. how to prevent self discharge as much as possible
4. what is the best use on low temperatures (sometimes if I am outside and is cold my camera wont want even to start and if I come inside the batteries restores and the camera is working ; is there a way to make the camera work at that low temperatures (0 C) not fully charged ? )
5. the charge cycle of NiMh is the same as charge cycle of Li-Ion (0% to 100% or 2 times 50% to 100% etc .)?

thank you !

On March 16, 2012 at 1:55am
Edward wrote:

1. if the battery voltage is above 1.2V, you will not damage the battery even keenp them empty over one mouth.
2. The charger can auto-stop the charge process is the battery is fully charged ,So do not worry about
3.we advise to keep the battery in cool to prevent self discharge
4.low temperature will make the battery work unnormally, We advise you warm the battery before use
5.yes there is no diffenence

On March 22, 2012 at 4:19am
norshah azwan wrote:

if the battery is at 70% of capacity and I begin charging , is this damaging it ? ( same question, George )  smile

On March 27, 2012 at 8:08pm
John wrote:

Hi

I have a customised NiMH battery of 12V 18Ah (2 x 5 M size NiMH cells) and it is charged constantly 8 hours a day by an alternater. We realise that contant charging is not good for it so we want to get a battery charging card which trickle charges it. Would you be able to recommend some battery charging cards which would be suitable for this battery?

On April 2, 2012 at 12:35pm
george wrote:

hi I have 4 nimh AA batteries of 2500mah (use for my camera) and those have a problem : until last week I charge them with a smart charger that have only 2 chanels ...with -deltaV protection , hight temperature protection..and timer protection ...
recently I bought a smarter charger with 4 chanels and damaged battery protection , and it sems that 3 batteries are damaged (and this charger don’t charge them) ...
how can I restore them (I know that is posible with an analyzer but I don’t afford one)

thank you !

On April 3, 2012 at 6:50am
Edward--CORUN battery wrote:

I am not sure if the batteries are damaged or the charger do not charge the batteries because you damaged the protection? I advise you to charge the batteries with the 2chanels (the 2 chanels charger is work well) if the batteries can be fully charged , that means the batteries are OK and the 4chanels charger is damaged.

any enquiry about ni-mh battery, send the email to zzrm316@163.com please

When you need the imformation about ni-mh batteries ,Do Not forget Edward from China

On April 3, 2012 at 10:14am
George wrote:

thank you Edward but not the charger is the problem because I have another new more advanced Charger fomam SAnyo enelop (mqr06) and the same problem ; I have also another 8 working batteries , those it charges with all my three chargers ;

I also have a question : can I put in my camera batteries with different capacity ? ex 2 of 2500mAh and 2 of 2700mAh

On April 3, 2012 at 8:12pm
Edward--rechargeable battery boy wrote:

Dear friend

You’d better not to use the different capacity or different brand rechargeable batteries in the unit at the same time . which maybe lead to over discharge and over charge to the rechargeable betteries.

As you know overdischarge and over charge will damage the battery cycle life.

Edward
zzrm316@163.com
rechargeable battery boy

On April 7, 2012 at 5:57am
James Japp wrote:

I was charging AAA cell on a dumb charger that charges at 0.05C (I checked this, 35mA for a 900 mAh cell). When I connected the battery the voltage was 1.37V, but after only a few hours the voltage got up to 1.63V. Is this bad? What is the maximum allowed voltage for NiMH cells and should the charger have some sort of voltage control?

On April 11, 2012 at 7:20pm
Edward wrote:

Firstly, I do not think the charger you chose is reasonable for the 900mAh battery. It will take too long time to fully charge the battery—30 hours at least !!it is normal that the ni-mh battery voltage up to 1.63V when it is connect with the charger .and it is fully charged when the voltage up to 1.63V if the battery is OK.you can send some battery and charger photos to my Email for my detail analysis
Edward
zzrm316@163.com   rechargeable battery boy

On April 16, 2012 at 11:54am
James Japp wrote:

That cell is cheap low quality Chinese or Turkish (brand C.F.L.) cell that certainly doesn’t have 900 mAh. My MP3 player that draws about 90-110 mA only runs for about 1h45m on that cell, but it doesn’t fully discharge it. After it shuts down saying that the battery is flat, the cell still has about 1.18V when loaded with 5 ohm resistor. I never bothered to measure the capacity accurately (I’d have to use a stopwatch for that because I don’t have battery analyzer), but it’s safe to say that it is half of the rated value, so 35 mA is reasonable current. Sorry I forgot to mention all this in first post.

The “charger” is a simple wall plug with open circuit voltage of about 6V and a resistor to limit the current. I terminate the charge when I estimate that the battery is full. I also charge two or three cells in series on this charger with a lower resistor value.

I’ve read several articles on recharging NiMH and they all say that slow charge at about 0.1C (or 0.05C) is OK, but none of those articles mention the voltage. Can these cells be damaged by overvoltage even if the current is kept low and what is the maximum safe voltage for NiMH cell? Should the slow charge be terminated when voltage reaches certain point?

On April 16, 2012 at 2:29pm
Ben wrote:

I am working on a school project involving charging 4-AAA NiMH batteries, 1.2V each, with a small solar panel used for outside lighting. The solar panel being used is a 12V 40mA solar panel. There are restrcitions on the size of the solar panel that can be used. The batteries are charging in series. Would it be better to use a solar panel that had a lower voltage rating and higher current rating, even if the to total output power of the solar panel is less. I was thinking that an incease in current would cause the batteries to charge faster

On April 16, 2012 at 11:04pm
Edward wrote:

different charge current need different max voltage to cut off the charge. generally speaking. the max. voltage should not more than 1.5V when charged by 0.1c and not more than 1.56V when charged by 1C. if you have more details to know ,please send to my email
zzrm316@163.com  
Edward

On May 1, 2012 at 2:24am
Azli wrote:

i read manual from my B65A+ multi charger (made in china) allowable fast charge current is 1C-2C (depend on performance of cell) and cut off discharge voltage is 1.0V/cell. My question is

1. how we going to know which battery use with which charge current.(ex. 0.2C, 0.5C, 1C or 2C)
2. if my battery capacity is 1800mAh and i,m going to charge with 1C. Is it mean my current setting shall (1*1800 = 1.8 A).
3. if the value above (1C-2C, cut off 1.0V/cell) wrong, so what are the value actually

Thanks

On May 15, 2012 at 8:54am
Roy wrote:

8.4v PP3 type 170mAh NiMH back-up battery within an intruder alarm system. Since the mains supply is very reliable (to date!), the battery is almost never utilised. It’s currently kept on float charge via a 560 ohm resistor from a regulated 9.6v supply. Since I read that a trickle charge rate of C/300 is recommended, would a higher value resistor help to increase the life of the battery? If so, what value should that series resistor be?

On May 17, 2012 at 7:09am
Edward--rechargeable battery boy wrote:

Dear friend, the existing charging current is 9.6V/560 ohm=0.017A=17.1mA about 0.1C ,
for long time trickle charge, we recommend from 0.03C to 0.05C, So you can higher the resistor value or lower the charge voltage to increase the life of the battery . In my opinion, the battery is very cheap , why not change the battery is it do not work well…It is not a easy job to change the charge method.
zzrm316@163.com Edward

On May 18, 2012 at 3:08am
Roy wrote:

Thanks Edward for that informative reply. I think I’ll increase the resistor to around 1k5.
In fact, by design (it is part of an intruder alarm!), access to the battery or the other components is not made easy, so I want to prolong the battery’s life as much as possible.

On May 18, 2012 at 6:10pm
Edward wrote:

Roy It is my pleasure ,Any rechargeable battery problem ,just contact with me.

zzrm316@163.com Edward

On June 20, 2012 at 6:37am
80'tronic wrote:

“VooDude: The statement that NICd chargers aren’t good for Ni-MH cells does not take into account the four-fold increase in cell capacity that took place over the time period where Cadmium cells were displaced by metal hydride cells.”

Is there any comment on this? I have a NiCd-era ‘overnight charger’ for 4xAA cells, which cranks out whopping 50 mA current. It takes some 2+ days to charge modern high capacity cells.
Is there any harm in using such a slow charger, even if the charger is forgotten on for a few days? How about Eneloop cells - are they more sensitive?

On June 21, 2012 at 2:57am
Edward wrote:

Generally speaking ,Ni-cd cell have lower capacity than ni-mh cell, So the ni-cd charger have low charge current, low charge current have no harm to ni-mh cell but waste your time .
For ni-mh cell ,do not over charge , even very low charge current will damage the ni-mh cell if you charge it over time
any cell or charger enquiry.  please contact me

zzrm316@163.com Edward

On July 30, 2012 at 7:35pm
M.Nagarajan wrote:

How many Ni/Cd cells (failure) can be replaced per used battery? Is any specified limit for replacing the cell per aircraft NiCd battery.

On July 30, 2012 at 7:39pm
M.Nagarajan wrote:

What is the market potential for Li-ion and Li-polymer batteries in aircraft application

On August 1, 2012 at 7:33pm
Edward wrote:

M.Nagarajan ,I can not understand clearly what you said ,would you please email me for detail information zzrm316@163.com     Edward

On August 14, 2012 at 2:21pm
Antonia wrote:

We have a pager system and we are using a multi unit charger and 1.5 V AA NiMH batteries.
The pager company suggests to charge the pagers every 2 days for not more than 15 hours.
My question is: what risks are there if the batteries are charged for longer than that?
Is there any possibility or recommendation for a different charging cycle (i.e. different batteries)?

On September 29, 2012 at 5:12am
Rob D wrote:

I have an 8 AA cell battery pack in my RC transmitter that I want to charge with my multifunction “icharger 208B” battery charger.

The more I read you excellent website, the more I realize how little I know about batteries and how dangerous my limited knowledge can be.

4 of the cells in the pack are 2100mAh Ni-MH 1.2V and 4 of the cells are 2000mAh Ni-MH 1.2V

I can set the current limit only on my icharger 208B charger.

So, my questions regarding my battery pack:
1: What amperage current limit should I be charging this cell pack at?
2: Should I discharge before charging?
3: As I do not know a thing about C ratings of values, can you please give me the answer in amps or milliamps and tell me if and how this amps answer relates to a C number, if at all?
4: What voltage should I expect to see the auto cutoff at?

Thanks
Rob

On October 9, 2012 at 12:35am
Edward wrote:

Dear Rob

1. you would better charge your ni-mh AA2000mah and 2100mah from 200mah to 400mah
2.,do not need to dicharge the cells if your charger have the max voltage control ability
3. about the C rate, it means the charge current/ the capacity of the cell. For example. if your charge the ni-mh AA2000mah 1.2V cell at 400mah current, then,the charge C rate is 400mah/2000mah=0.2C . For better life performance, I advise the charge rate is 0.1C to 0.2C,and the charge time is 12h to 6h
4.I advise the max voltage should control at 1.45V for each cell

On October 18, 2012 at 12:58am
XFM wrote:

1 - How safe for battery life is to maintain trickle current (say C/50) indefinitely for months, in order to have the battery always full charged to be ready for immediate use?
2 - We achieve a C/50 average trickle current by pulsing a C/3 current during 1.2 ms of the time of a 20 ms PWM cycle . Is this equivalent to apply a constant C/50 trickle current? Is 1.2 ms enough to allow current charging the battery?

Thanks

On October 20, 2012 at 7:16am
Edward wrote:

Dear XFM

your question is not easy to explain ,please email to me for details
Edward
zzrm316@163.com   rechargeable battery boy

On October 23, 2012 at 5:31am
leon wrote:

Thank you for your excellent article..I have a 7.2v 6cell nimh battery

I can set the input current..but not a maximum cut off voltage…I am manually switching the charger off when I have a reading of around 8.6v.

Is this OK, and what should the maximum voltage showing on the charger..

I am thinking about 1.45v per cell.

Many thanks..Leon

On October 23, 2012 at 6:29pm
Edward wrote:

please tell the capacity of the battery?

On October 24, 2012 at 2:37am
leon wrote:

Thank you…I have 2 batteries…

1x1800…..1x3700

On October 24, 2012 at 6:50pm
Edward wrote:

if you use the max voltage at 1.45V /cell to control the control , I advise you to charge the batteries at 0.2C rate, and record the charge the time ,if the charge time exceed 6hours, please reduce the max votage to 1.43V and try again, because different battery from different factory have different charge max voltage

On October 26, 2012 at 1:31pm
Hank Roberts wrote:

Can you comment on what to look for/check in a batch of unknown cells, and which cells are worth keeping and which should just be recycled?

Tenergy right now is closing out old-dtyle NiMH cells (light blue wrapper, lower case “e” on the label).  I’ve bought several dozen from different closeout places hoping they’re ok. 

Most of them arrive showing about 1.0 volt.  Those seem so far to recharge OK (except on a Maha charger, which shows “HIGH” for every single one, and won’t charge them). 

Others arrive showing 0.4-0.5v and won’t hold charge more than a day or two; some of those get very hot.

On October 29, 2012 at 2:26am
Edward wrote:

Dear Hank Robert
Do you mean how to check it is Ni-mh or ni-cd??
in my opinion, the cells’ voltage should be more than 1.2V
How can you accept the cells showing 0.4V-0.5V?

On October 29, 2012 at 7:49am
Gabriel wrote:

I am getting into rebuilding hybrid vehicle battery and it requires to sort cells from different
batteries, mostly panasonic prismatic 7.2v 6500mah in a series array of 38.
Can you tell me the best charging /discharging C rate ,termination method,number of rejuvenation cycles and best sort procedure.

On October 29, 2012 at 8:28am
Hank Roberts wrote:

> Do you mean how to check it is Ni-mh or ni-cd??
No.  I described them by brand name and appearance above.

> in my opinion, the cells’ voltage should be more than 1.2V
I agree, if they were new stock I"d expect that. These are half price.

I’m asking about a particular cell widely available right now in closeout/discount sales, half price. 

Conclusion—some seem OK, but batches are probably not worth buying, from my experience so far.

> How can you accept the cells showing 0.4V-0.5V?
I complained and got some money back on one batch, apparently the closeout place knew they were a mixed lot —but the replacements are in the 1.0v range. 

I’m asking if these cells that arrive showing 1.0v are worth trying to put into regular use.  So far, they seem to hold charge for at least a week or so—checking with a ZTS tester.

The ones that showed half a volt before charging will charge up, and work OK for a few hours’ use in a LED flashlight _if_ used immediately after charging; but lose their charge within a day or so.

I’d guess Tenergy dumped old or poorly stored cells cheap: 
Again: light blue wrapper, lower case “e” on the label, NiMH. 
These aren’t currently shown on Tenergy’s website, apparently discontinued.

On October 29, 2012 at 3:21pm
Gabriel wrote:

The batteries are NIMH 6X1.2 6500 mah

On October 30, 2012 at 7:45am
Hank Roberts wrote:

Short answer from more recent experience—don’t believe a voltmeter, a badly degraded battery can still show one volt.

I used a ZTS battery tester, which puts a load on the cells.
That showed the Tenergy light blue cells had no useful capacity left.

On November 8, 2012 at 4:47am
Boris Kranjc wrote:

I have NIMH battery for RC car, 6 cell, 7,2V, 2000mAh

I should charge it with Imax B6 Charger.
I’m not sure that information given with this charger is right, because it says that charge current for this exact battery is 5A, what seems much (attached manual – page 33).
And according to your words it would be better to charge with 200-400mAh. Fast charge would eventually be (if i,m right) 1C or 2A.

On November 12, 2012 at 9:21am
sonspit wrote:

my nimh 7.2 1100mah used to get warm when i charge it.. but now its cool no warmth at all.. does this mean its not charging///

On November 12, 2012 at 6:07pm
Edward wrote:

what is the charging current and the charging time? if the charging current is low and the charging time is not long, the battery will be cool also.

On November 16, 2012 at 12:46pm
Frank wrote:

Hi, I have a 8.4V 1200mAH 7 cell airsoft battery.  I recently tuned my gun and tested it out with this battery.  The gun fired rapidly at first then the rate of fire gradually dropped until it came to a stop.  I measured the voltage with a multimeter and got around 9.28V.  I wonder if that means my battery is fully charged, half way or in need of a charge in order to run my airsoft gun.  Please let me know, since if my battery is good, I would need to open up the gearbox and spend hours retuning my gun.  Thanks.

On November 18, 2012 at 9:43pm
Edward wrote:

if the ni-mh cell fully charged, the voltage should be above 1.35V in one hour.
so, just try to continue to charge your battery.
in addition, would you please tell what is your gun?? I am afraid about the battery cycle life
is not very good for your gun.
please send to my email
zzrm316@163.com

On November 20, 2012 at 9:33am
Nick wrote:

I am trying to figure out a way for charging 3 batteries in a 4 battery charger, or 1 battery in a 2 battery charger. The only thing i was able to think was to construct a dumb battery consisting of two diodes in series. They should be connected to conduct current, and as the total forward voltage drop is 1.4 volts, the charger will shut off when the actual battery voltage reaches 1.4 volts, as the total voltage is 2.8 volts. I have not tried it yet, and I would be very obliged if you could tell me your opinion about it. I wonder also if I could do the same thing with a zener diode. I you can think of something better please let me know.

On November 21, 2012 at 1:31am
Edward wrote:

why not set the each charger channel for each cell independence??
or,  the charger have to test the volagage from the charger, take 2battery charger for example: if the charger test the voltage is above 1.6V from the channel when the cell(cells) put into. then the charger know 2cells in the charger, and it can control the max voltage is 2.8V, if the charger test the voltage is less than 1.6V from the channel when the cell(cells) put into. then the charger know 2cells in the charger, and it can control the max voltage is 1.4V…but there is a problem , if there is a bad cell is 0V, the charger can not judge 1or 2 cells in the charger

On November 21, 2012 at 3:15am
Nick wrote:

The battery chargers I am talking about are not intelligent chargers. For this reason they cannot figure out from the battery voltage if one or two batteries are charging. Actually if you connect one battery it will not charge it at all because the batteries are connected internally in series, so it will pass no current at all. So I have to replace one battery with a circuit that will make the charger believe that there are 2 batteries connected. The idea is that the charger will continue to charge the 1 battery (in series with the dumb battery) till the total voltage across them reaches 2.8 volts, and then it will cut off the current. (the voltage drop across the series connected forward biased diodes will be in the vicinity of 1.4 volts, so that the remaining 1.4 volts will be at the terminals of the actual battery when it will be fully charged).

P.S
I accidentally pushed the “stop receiving notifications for this comment” button, so please reset it if possible.

On November 26, 2012 at 11:12am
John Highet wrote:

I have a velomoibile (human powered aerodynamic tricycle) which uses a 3800mAH 12V NiMh pack to run its electrics. I have a German (ACS 110) smart charger which I plug in randomly to recharge the unit. I’m thinking of fitting an LED based high-accuracy voltmeter to monitor the battery and let me know when to charge it. What would be a good general threshold for re-charging? (I’m aware that the voltage/time graph drops very steeply before the battery goes flat.

On December 6, 2012 at 8:22am
Mike wrote:

I have a Energizer Quick Charger for Ni-Mh batteries. I can’t get my other Ni-Mh batteries to charge in it. The red light starts blinking when I put a single battery in or multiple batteries in. It charges the Energizer batteries that came with it just fine.

My other Ni-Mh batteries are from various mfg’s and are brand ne. I can’t figure out the reason for this. Could there be some kind of coding between the Energizer batteries and the charger?  Clues, anyone??

On December 7, 2012 at 7:39am
Ed wrote:

I do not think there is any code or password between the englizer batteries and the charger. May the other cell is a bad cell. So the charger can not identify it.
Do not use the different rechargeable battery in the same charger or unit

On December 7, 2012 at 8:03am
Mike wrote:

Ed, Thanks for the reply.
I have tried each cell individually. They are all brand new. They charge good in my slow charger. I do not use different cells in the charger at the same time.
I thought maybe it was the milli-Amp hours rating (mAh). The charger will work with 2200 and 2300 mAh batteries but the ones that I am trying to charge are 3000 mAh.

Just frustrating since the slow charger takes a long time.

 

On December 11, 2012 at 1:31am
S D wrote:

I want to ask a silly question. Is it okay for me to use a battery charger which shows a rating of 1.5 V to recharge Ni - MH batteries of 1.2 V rating?

On December 11, 2012 at 4:53am
Ed wrote:

when the ni-mh battery fully charged ,the max voltage can reach about 1.5V ,So you can charge the ni-mh battery with your charger showing a rating of 1.5V.

On December 11, 2012 at 7:37am
S D wrote:

Thanks a lot, Ed.

On December 12, 2012 at 12:15pm
Tim lumsdon wrote:

Hi,
I have a 14.4v nicad 1.2 amh battery for my draper electric drill,  the nicad pack has gone to heaven and will no longer hold a charge.
I want to buy 2 packs of 7.2v nimh 2 amh Nimh batteries, if i put these in series can i charge them from the 18v 400 mah charger that came with the drill (i.e. nicad charger)

How long would i need to leave them before disconnecting the charger

Thanks

 

On December 20, 2012 at 10:01am
Peter Kendall wrote:

Dear Edward, My son has a Xootr powered scooter, with a 24volt NiMh 3200 maH battery pack inside. He bought it without a charger, but it came fully charged, so we know it works. I have purchased 2 different NiMh chargers, but they will not recharge the pack. I think it must be due to the temp. sensor that both these intelligent chargers use.

Can you describe how the connection between the pack and the charger works? I believe the charger refuses to charge until it sees some sort of signal or conductivity from the sensor wire. Neither charger comes with any instruction as to how to connect this third conductor!  Thanks very much!

On December 23, 2012 at 7:39pm
Edward wrote:

Dear Peter, I advise you tell me the brand of the Xootr powered scooter, or more detail information about the scooter…the charger and the battery have very complicated relationship. and I advise you contact with the scooter company for help

zzrm316@163.com

On January 2, 2013 at 10:12am
kushal shinde wrote:

Hi Edward
i have a Ni-MH battery charger, 4 cell. It can charge 2 or 4 batteries at a time. I want to modify the charger circuit, so that it would be possible to charge a single Ni-Mh battery.
can you pls advise what circuit modification i can do to achieve this without damaging the charger.

On January 4, 2013 at 12:12am
Edward wrote:

Dear friend ,No No NO ,NO NOT DO THAT, because the charger have the voltage for 2 or 4cells control. You’d better to buy a charger that can charge one cell

On January 6, 2013 at 11:09am
John Friar wrote:

I have owned for 5.5 years a 1999 Ford Ranger electric vehicle that uses 39 x 8V NiMH Panasonic batteries (312 V nominal).  The charger is built into the vehicle.  Ford instructs to leave vehicle on the charger when not driving (in part, for battery temperature control (I live in MA)).

I bought the vehicle at with about 8K miles, now has 26K miles.

Each winter, the “miles available” is less than summer (Nernst equation, for sure), but this year the reduction is greater.  Also, the battery behaves as expected for the first quarter-charge, but falls off rapidly as soon as it goes below 75% charge (I’ve heard that this happens to some batteries).

What problem(s) does this suggest?  (I spoke to a local battery distributor franchisee who says he can test the performance of the individual 8V batteries if I bring it to him, but that requires removal of the one-ton pack, so I’m looking for information before doing so.)

Thanks!

J. Friar

On January 6, 2013 at 6:21pm
Edward wrote:

Dear friend, the battery distributor franchisee is right, I think some individual 8V battery pack can not work well

On January 6, 2013 at 10:52pm
RIck wrote:

Edward, what is your view about frequent “topping-up” with nimh (AA) with regard to cycles the battery can do?

My thought is, with the battery loosing about 10-30% first day out of the charger…  In theory, one could apply say .2c for an hour every day (or shorter if it hits NDV termination) and give it back 20% daily.  So, a non-LSD can stay fresh every day.

I have read that shallow cycle with Li-ion works well without burning up the cycles.  This article further suggest the math is charging merely 20% will burn up 20% of a cycle.  So, a 100 full-cycle is the same as 500 20% top up cycle.

In your opinion, do you think the math is similar with Nimh?

Thanks
Rick

On January 7, 2013 at 1:28am
kushal shinde wrote:

Hi Edward can you suggest some good AA Ni-Mh battery chargers which can charge a single battery.

On January 7, 2013 at 7:40pm
Edward wrote:

Dear kushal shinde ,you can try GP UNIROSS ANSMAN DURACELL energizer and so on

please get more details about the charger before you buy

On January 7, 2013 at 7:45pm
Edward wrote:

Dear RIck, the math is similar with Ni-mh, you can refer this from IEC62133-2 about the cycle life of the Ni-MH battery

On January 7, 2013 at 10:04pm
Rick wrote:

Thanks, Edward.  That is informative.

I am thinking about converting my old battery killing dumb charger into a timed battery refresher. Had partial re-charge use up a cycle as a deep discharge/recharge, I would drop the idea of cooking up a time-based refresher.

Speaking of old…  As I get older, my memory gets worst but my old NiCd’s memory keep on getting stronger.  If only I am more like a NiCd battery, I could remember that…  Never mind, I forgot what I could remember.

Thanks again for the info, Mr. Edward.

Rick

On January 16, 2013 at 7:14am
Austin Ratnam wrote:

I am attempting to power a small circuit drawing around 100mA max with 6, 3100mA non protected li-ion batteries in series providing 22.2v. The batteries are to be connected to a 6 cell pcm (protection circuit board) through which the circuit will draw the supply. The PCM board can be adjusted for max discharge current.

What would be the ideal maximum discharge current I should set the pcm to then?

0.1C or 0.05C? (roughly 310mA & 155mA respectively) Is there any significant advantage of setting it at 0.1C over 0.05C?

 
   

On January 28, 2013 at 8:16am
Andrew wrote:

Hello.
I am trying to charge 1600mAh ni-mh 9.6 v battery with a simple solar cell and have a few questions:
1.  At first we were worried about the battery exploding. Is this a possibility given the low current provided?

2.  Do I charge the battery with 9.6v or 1.2v since that is the charge on each cell?

3.  Given the low current, it will be difficult to determine when it is done charging.  It does not need to fully charge each time for this application. At such a low current, how would you advise detecting when it is full enough?

4.  We have not picked out the solar cell yet, but it needs to be cheap. 24 hours to charge the battery would be fine since it will not be fully discharged each time. Do you have any recommendations on voltage and current to get?

Thank you for your help.

On January 28, 2013 at 9:49am
Rick NJ wrote:

Andrew,

I am not a battery expert but battery “informed”.  Until someone with better knowledge comes along, here is what I can suggest:

——-

Q1.  At first we were worried about the battery exploding. Is this a possibility given the low current provided?

Since you are talking NiMh, it is unlikely it explodes particularly with such low current.

——-

Q2. Do I charge the battery with 9.6v or 1.2v since that is the charge on each cell?

Since you said this is 9.6v, I assume you are accessing it as a pack (of 8 cells in series) rather than each of the 8 individual cells.  When you are accessing it as a pack, you charge it as 9.6v.  However, If you are breaking the pack up (physically, or merely connecting to each cell individually), then you charge it at the cell voltage as 1.2v.

Either way, your charging voltage needs to be higher than the pack/cell voltage.  For a 1.2v cell, 1.8v-2.8v works nicely.  For 9.6v, I use just a bit over 11’ish to 13v works nicely.  I can pump 1C into my 11volt battery at 13volt.  (1C is to charge 1-watt-hour battery in 1 hour.)  At lower current, you don’t need as high a voltage (wastes less).

You can look at it this way: Current is what got stored, but Voltage is what pushes it in.  If you spend all your energy pushing, very little energy is left after you got in.  So, if you set your 1watt panel output to twice the voltage needed, you get only 1/2 the current to be stored.  Of course, the battery is not 100% efficient in converting the power into chemical energy for storing.  You push in 100maH, the battery probably stores about 2/3 or 3/4 of that.

——-

Q3. Given the low current, it will be difficult to determine when it is done charging.  It does not need to fully charge each time for this application. At such a low current, how would you advise detecting when it is full enough?

NiMh termination is typically based on NDV (negative delta voltage) of about 5mV.  You need pretty good circuitry to detect 5mV out of 1.2.  dT/dt or dV/dt are other methods.  All those require fairly complex electronic.  So, you either use your solar panel to power a consumer-charger wasting energy converting, or you do estimation.

If your battery is say about 8 good AA cell, you will be talking about 16-20 WH (watt-hour) of power.  If your solar panel is 1Watt, it will take you 16-20 hours to charge it full.  You can estimate based on that.

——-

4.  …. not picked out the solar cell yet, but it needs to be cheap. 24 hours to …… Do you have any recommendations on voltage and current to get?

To charge 9.6v, a 12-13volt source should work nicely.  Volt multiplied by Current is your Watts.  So, 12Watt panel will give you 1A at 12volt.  The wattage you need depends on your battery size.  You need at least 1/10.  If your battery is 8 AA batteries as in my example in Q3-answer, 16 to 20 watt-hour storage needs around 1.6 to 2 watt-hours (if you have 10 hours of sun where you live).  Much below 0.8w (1/20 of 16), you may not have enough current to even make a dent.  You are loosing all the energy in the transfer, conversion, etc. and nothing to store.  So, to charge at 1/10 for 10 hours but you have only 5 hours of sun, you need to double the panel’s wattage.

If you want it to be cheap, ahem, you are looking at the wrong solution.  To charge and discharge daily, you will likely spend many times over on the panel and batteries than say a good recharge battery with high capacity and high cycle – say one with enough power that you charge once a month with a normal AC plug in charger.

I use a few solar sidewalk lights on my lawn.  Each year I need to replace my battery because of over-discharge and rough environment outdoor.  Money-wise, I am better off using regular AC recharge with but for the trouble of charging or changing battery.  I am actually considering converting it to AC charge with an all day-trickle (1/20C).  With AC recharge, I wont have to clean the darn solar panels on those lights anymore.  Such a pain – after a few weeks, they are clouded and the lawn dust (pollen, grass bits…).  If I don’t clean it every month, the batteries are undercharged even in the summer and so it over-discharge every night.  Even with regular cleaning, a few days of no-sun send the batteries into over-discharge (and thus convert itself to garbage a bit at a time and killing itself in less than a year.)

On January 29, 2013 at 8:36am
Edward wrote:

Dear Rick NJ , You are so professional at the solar panel and the Ni-MH battery from your suggestion! very good! I my email is zzrm316@163.com and i am an ni-mh battery engineer for many years. hope to contact with you often

On February 8, 2013 at 1:48am
Herman wrote:

For new batteries my Maha MH-C9000 charger advices the “break in” charging function with 0.1C. So I started this process with a set of brandnew Eneloop XX. To my surprise, the batteries (which were presumably almost fully charged) first received a charge that is more than their full capacity, given me the idea of heavily overcharging. On the other hand, the tension of 1.49V is not too high (at this moment the 900 mAh batteries received 1050 mAh and still charging).
Can anyone explain why the charger choses for this behaviour?
Thanks, Herman

On February 13, 2013 at 4:50pm
Rob Decker wrote:

Edward:

I am hoping you might be able to help me out…

I am trying to create a solar-powered bicyce light using NiMH batteries.

My problem is, though I’m learning, is how this all fits together!

I am trying to create this light with an optimal combination of:
- small physical size
- easily recharged (solar)
- long run times
- ultra bright lights

I have found a solar cell for battery charging that seems to be middle ground in terms of Volts (5V), Amps (40mAh) & physical size (58mm x 39mm), which works well with my design.

Batteries are an area where I could really use your help. I was all ready to settle on NiMH, until I found Low Discharge NiMH…and then the new LiFePo4 batteries.

My design concept is to keep this as small as possible. Physically, there is room for any combination up to 3 AA batteries, but as batteries will likely be the greatest expense, using one or two, or using a less expensive type of battery, would be best.

So, here are a bunch of questions I hope you might be able to answer and shed some light!

What do you think about Low Discharge NiMH? Not everyone uses their bike every day, so it would be great if the batteries wouldn’t drain out because of non use. Or should I look at a high-capacity NiMH?

NiMH batteries usually say 1000 charge cycles. But what happens if the solar charger is constantly cycling on and off trying to top off the battery? It would be nice to get 1000 days, or nearly 3 years out of the battery…but I’m concerned that every day use might impact the number of charge cycles.

Also, I assume there needs to be some controls in place to not overcharge the batteries?

Can I use a solar charger to charge a Lithium Iron (LiFePo4)?

I don’t know what the appropriate mAh should be, given that I am trying to keep this light as small, bright and powerful as possible—so I know there will have to be a tradeoff somewhere. I am planning to use two LEDs that will draw a total of 40mA.

So, any help you can offer would be greatly appreciated!

Thanks,

Rob Decker
rdecker@x-media.com

On February 17, 2013 at 1:39am
Jerry wrote:

Hello Ed, glad I found this site.  My kids go thru AA batteries like crazy and I have been buying energizer nimh and others that have capacity from 2300 to 2650mah.  Over time, the batteries stop charging on a 15 minute charger so I built my own microprocessor based charger with computer interface for secondary control and logging.  It seems that if I deep cycle the batteries a few times the will start charging n the 15 minute chargers.  Some have lower voltage (less than 1v) when charged and again, deep discharge followed by rapid charge seems to heal them.  The questions I have are around charging algorithms as I’ve been using 2.4amps which is approximately 1c.  This sounds high by your standards so I might ( with your confirmation) cut back to .5c.  What I notice though, is most batteries heat up with a dT/dt greater than 1 degree per minute at even .5c and they are nowhere near charged.  These are all the same brand with varying dT/dt.  Are these batteries shot?  Also, at .5c, it seems like people chart better NDV drops than 5mv per cell.  So what is the best NDV per cell at .5C and 1C?  My charge software currently looks for 10mc NDV with a max temp of 140F and plan to add dT/dt as well but again, my experience is most batteries will exceed our 1 degree per minute even after stabilizing at 5 minute precharge.

On February 17, 2013 at 1:46am
Jerry wrote:

One other question: for nimh batteries in the 2400mah range, what would you consider is a good stabilizing precharge at .5c time?  The precharge gives the battery time to stabilize both temperature and voltage.  I am using constant current obviously.  I’ve thought about using pulse charge at either .5c or 1c with a lesser duty cycle in my precharge as well.  Any thoughts on this?

I know this is asking a lot, but is there an ideal algorithm out there for nimh batteries in this capacity charged as single cells?

Thanks, you articles are very informative!

On February 17, 2013 at 8:02pm
Edward wrote:

Dear Jerry ,It seems to me you are very professional at the ni-mh battery.  in my opinion,NDV keep 5mv per cell at .5C and 1C will good to control the charge cut off.

check the bad cells have lower voltage (less than 1v)  and analyse if the cells if ok or bad.

On April 4, 2013 at 11:33pm
Jacques wrote:

I am building a battery backup system/charger using Ni-mh batteries. (I know lead acid would be better but I need to use Ni-mh). Would it be ok if I charge them with a constant voltage/current limited charge. I suppose the cells would not be overcharge if I limit the voltage? But also I would not get full “potential” out of the batteries? Would the cell reach full capacity over time?

On April 5, 2013 at 11:34am
Jerry wrote:

I’ll reply to Jacques but Edward would be more professional:

Jacques, 

If you use constant voltage with current limiting, and the current limit is held to no more than .1C, then you will be safe charging the batteries and will reach 100% capacity.  You should use a temperature monitor as well just to be safe.

This all assumes that you run your charging circuit so that the current limit is held at all times.  If the current limiting circuit is not activated, then you will be running in constant voltage mode and this is not safe on the high end, and wont allow the batteries to reach full potential on the low end (of charge current).

Also, circuits to limit charge to .1C are very easy to build using an LM317 regulator with a current sense resistor in series with the load, tied back to the common.  The LM317 will maintain 1.25V from output to common, using this voltage of 1.25 divided by .1c, you can set the sense (and current limit) resistor to any practical charge current up to 3A, assuming the lm350 is used instead of a 317, or up to 1.5A for the 317. So I wouldn’t rely on a current limiting circuit from a power supply when you consider you can build a better charging circuit for less than $5USD.

Some curent limiting power supplies work very effectively as a charger, again assuming the current limit is variable or known to be maintained at less than .1C. if the current limit is higher, you can use a timer to limit the charge time but this is risky and must be used with a temperature probe.

Jerry

On April 10, 2013 at 10:46am
Boris Kranjc wrote:

I need advise or help. Please Ed or anybody with experience!
I have Imax B6 charger and 2S 5000 mAh Lipo battery. When I set charger by instructions )Lipo-2S-7,2V-5000mAh cutoff-360 min cutoff, max 8,4V-5A charging or less 2A, 3A) it usually says “conection break”, or it starts to charge and It says “full” but each cell is at 3,5V. Weather I charge it or balance charge it doesen’t charge more than 3,5 V per cell.
Battery is brand new it is first charge after discharging in RC car. Car is set to cutoff at 3.0V, but it won’t go after I have driven it for 10 min.

On April 14, 2013 at 5:15pm
will wrote:

So to charge a battery, what current is applied to the positive and negative terminal?(negative current to the negative terminal or what?)

On April 22, 2013 at 11:15am
Dave wrote:

The article has completely wrong data!  Fast charging mode destroys the batteries. Why they write the bullshit? The want to make their sales pitch, or they are idiots. A slow charging device with automatic switch-off based on measured battery capacity will extend the battery life over 1000 cycles.

On April 22, 2013 at 9:14pm
Jerry wrote:

Dave, Your statement has no foundation with testing I have done and I assume Edward and others will agree.  Also, how do you determine initial charge or automatic switch off at full charge?  It can’t be done without draining the battery.  I have yet to see a reliable way to measure battery charge or capacity.  It can’t be done with voltage alone.  You have to measure the voltage drop over time and this varies so greatly by battery it is completely unreliable.

I have charts and data that demonstrate without a doubt that fast charging at .5C brings a battery up to full charge more reliably and efficiently than slow charge.  I have a number of graphs the show the convergence of dTdt with NDV and find it to be extremely reliable.  Also, by using dTdt, I can detect a rise in termperature much more reliably than slow charging.  My charger usually kicks off below 85 degrees F, which is consistently lower than most slow chargers on a timer.  Heat is what impacts battery life.  If you put a 80% charged battery on a 15 hour slow charger you will most likely exceed 85 degrees or as much as 100 degrees.

The charger I built has all all the normal safeguards like dTdt, NDV, timers, max capacity, initial voltage, max voltage, etc, etc.  It drops to .05c at full charge or can be set to do a .1C for an extra 30 or 60 minutes to top the battery off.  I have found Edward’s advice on this site to be beyond reproach for the practical and efficient charging of both NIMH and NICD batteries,

Jerry

On April 28, 2013 at 10:09pm
nikhil wrote:

hello ,
        i am trying to charge 12v 800mAH(1.2v*10cells AA) NimH battery. i am charging it with an lm317 as a constant current source . throughout the charging process the same current of 200mA(0.25C) is giving.charging start/stop and discharging start/stop is controlled by PIC. So it never goes beyond the predetermined value.
          my question is that during charging the battery voltage goes from 15 to 17.3v and so temperature . what might be the maximum voltage at this charging current and rate. And also which will be the better charge termination , a maximum threshold voltage or time. i don’t want to make my charger complex by making it an intelligent charger. i am also ready to compromise the charging rate because the charging time can be as long as 8 hrs.

thanks
Nikhil

On April 29, 2013 at 8:17am
Jerry wrote:

Nikhil, 

I assume you aren’t using a temperature probe so you are limited in what you can do with a smart charger anyway.  Also, at that charge rate it is somewhat dangerous to charge batteries as they can overheat and cause a fire.  I have done it myself and I am very knowledgeable about battery charging. 

Since you don’t have a temperature probe, the only thing you can do is set the maximum time to 6 hours using 1.5C total charge at .25C.  Maximum charge voltage would be 24v though many chargers are much more conservative.  The maximum charge voltage of 2v per cell would be considered an emergency type shutoff only, not an indicator of a fully charged battery pack.

Another approach that would reduce the efficiency of your charger would be to charge for 10 minutes and then stop, let the battery pack voltage settle for one minute, and then measure the voltage.  If the voltage meets or exceeds 1.41V (some recommend as high as 1.46v) then the pack is charged.  If the voltage is lower than 1.41v continue with another charge cycle.

I suggest you add a thermistor to your charger at a minimum.  If you do that, please come back and post as there would be other simple alternative ways to more accurately detect a peak charge and improve the efficiency of your charger.

Jerry

On April 29, 2013 at 10:24pm
nikhil wrote:

Hi Jerry,
          Thanks for your reply .
” the only thing you can do is set the maximum time to 6 hours using 1.5C total charge at .25C. “, sorry i can’t understand this statement . did you mean starts charging at 1.5C and reduces the rate to 0.25C at the end?

      Is it’s safer to charge at 1.5C(1.2A) which is much higher than 0.25C.My circuit never charges a fully charged or partially charged battery . it only charges a discharged battery , that’s why i choose constant time charging and avoid thermistor.

Also what might be the minimum discharge voltage for a 12v NIMH battery(load around 70 mA) ?

thanks and regards

Nikhil

On April 30, 2013 at 1:13pm
Tom Cox wrote:

I found a nice 14.4 volt Makita drill that someone threw away.  It has a 2.6 Ah NiMh battery.  But it has no charger.  A new charger is very $$$, and the money would be better spent on a a new drill - UNLESS I can use a power supply to charge it.  I have access to literally hundreds of power supplies at work.  For example, I just found a small 15v, 1.33 amp power supply, but it’s a switching power supply.  Can I use this, provided I don’t leave the battery unattended?  If not, what would be the proper rating for a P/S to charge this battery?  ( I realized that you do NOT recommend PS chargers for nickel based, but it’s eithr that or toss it.)  many thanks

On April 30, 2013 at 4:04pm
Jerry wrote:

Nikhil,

What I meant was that at .25C charge rate the recommended charge time would be 6 hours.  Again, I would recommend a charge rate of .1C to avoid overheating and a potential fire if you have the time available.  Then the recommended charge time would be 15 hours.  I was referring to the standard total charge of 1.5 times capacity for batteries, not that you charge at that rate. 

Again, thermistors are inexpensive and the PIC chip has A2D converter making them easy to sense temperature.  You are not charging at a high enough rate for a smart charger to detect peak on NiMH, but you can improve the efficiency and safety by using a temperature testing circuit.

Jerry

On April 30, 2013 at 4:20pm
Jerry wrote:

Tom,,

Every battery pack is different but I think it is safe to say a 15v power supply will not be high enough to charge a 14.4v battery.  Most likely that battery is bad and was the source of the failure.

Also, for NiCD and NiMH you need current limiting.  It is a simple circuit using an LM350 or LM317 and a resistor.  You not only need to exceed the voltage of the battery pack by a factor, you also then have to take into consideration the voltage drop of the charge circuit and cables, which would be generally in the 1.2 to 1.5v range.  So I would think a starting point of 18-20v would be about right for a 14.4v pack, but again, it depends on so many factors not the least of which is the age and condition of the battery cells.  Also, if you have a shorted cell in the pack, the voltage required will be lower which is wrong but hard to detect with unknown batteries.  Lastly, if you attach an unlimited current supply to the battery that has a low charge, it will easily exceed the 1.33A of your 15v supply. 

Look around your shop for a variable supply in the 24v range that also has current limiting.  A secondary approach, on the cheap, would be to try the 15v supply with an amp meter inline to check the current.  Keep the current under .26A and charge for 15 hours the first time.  If the cells do not keep 14.4v once the charger is removed, then you most likely have a bad cell.  Many 14.4v batteries exceed 17v when initially charged. 

My apologies to Ed as I have no intent to hijack his board.  I just love charging batteries and found the science, some of which is explained very well on this site, fascinating. Something with my OCD must kick-in when I see an uncharged battery.

Jerry

On May 7, 2013 at 12:48am
bilal wrote:

can u help me to make a rapid charger for 100A battery
plz help me in its circuit diagram

On May 10, 2013 at 1:39am
james wrote:

for a 6080Ah battery bank with 40%DOD what does charging at C/18 an discharging at C/48 gives us

On May 10, 2013 at 11:39am
Rick NJ wrote:

With 40% of the cell DOD (or with 4%), you get close to none until you removed the dead cells and rearrange the bank to give you the same bank-voltage.

Unless you have a very odd cell arrangement, I suspect the bad cells are distributed randomly in parallel and in series along with the good ones to form the bank.  The bad cells will pull down the voltage of the cell-bank giving you very little power.  I would not be surprised if the bank voltage dropped to below useful level in seconds.

Rick

On July 9, 2013 at 1:49pm
Frank E wrote:

The article rmentions a quantity C several times
viz a viz
charging at less than 0.5C.
charge of 0.1C
fast charge of 1C.
trickle charge is set to around 0.05C.
C-rate of 0.1 to 0.3C,

What is the witer referring to; Charge (Q )in Coulombs,? Temperature (T) in degrees Celcius? Capacitance (C) in Farads?

On July 9, 2013 at 3:39pm
Jerry wrote:

Frank,
C is the capacity of the battery in mah so .1C of 1000mah battery is the slow charge rate of 100ma.

On July 9, 2013 at 6:14pm
Frank E wrote:

Yes the author is definitely getting mixed up with SI and SI derived quantities and units then. or they have made up their own confusing quantities using SI / SI-derived symbols

eg “fast charge of 1C” reads to me fast charge of 1 coulomb which could be an Amp for a second, 10 Amps for a tenth of a second.

C isn’t capacity of a battery, C is Capacitance (ability of an entity to store Charge), two very different quantities.. 
Q or q is the symbol used for charge
1 mAh is 3.6C [1 coulomb is an Ampere Second A.s or As , coulomb ampere and second are all SI base units therefore an ampere hour = 3600C]

I is used as the symbol for Current not C.

It’s mAh not mah. mA, not ma.

On July 10, 2013 at 10:58pm
Boris Kranjc wrote:

i have 5000mAh lipo 2 cell, 7,4 V battery. one cell was totally discharged and shows 0V. I suppose it cannot be fixed, only replaced?! Other is good.

On July 17, 2013 at 2:50am
Maurie Withers wrote:

What is the best charger for a YAESU FT-60 HT radio battery rated at 1500ma and 2200 ma-which are brand new and I would like to charge them correctly.Thank you Maurie

On July 17, 2013 at 5:44pm
Jerry wrote:

Maurie,  You should use the supplied charger which is a slow charger I believe not unlike those for my HT’s.  Generally, without a sophisticated circuit (which would be easy for you to design/build or replicate based on you being an amateur operator) it is best to charge each battery at a constant rate of .1C, C being the capacity of the battery contrary to Frank E above.  So a constant current of 150mA for the 1500mA and 220mA for the 2200mA would give you the recommended charge rate of .1C.

Most of the supplied wall wart chargers don’t do a really good job of current regulation for constant current and usually don’t provide the full .1C rate at first as that might require a higher voltage than it can supply.  It is easy to wire a constant current source using an LM350 regulator.  A fixed supply greater than 1.8x the battery voltage would do it as a source to the constant current circuit. 

Please note you should limit the charge time to 15 hours for .1C rates and also check the temperature occasionally.

C is generally used as it relates to batteries as being the Capacity in mAh’s, or milliamp hours.  In case Frank is still policing this site, please note I used the correct case for the ‘A’ in milliamp hours. Also, Frank, please note I can’t read this fine print so I might not have the correct number of ‘L’s in the term milliamp.

Lastly, Frank, just to clarify, the character ‘C’ is used for more than just capacitance and is generally used for battery capacity.  Look around and you will find it across the IEEE docs as well.  I will apologize for incorrectly not capitalizing the ‘A’ in mAh in my rush to answer Frank’s question. 

At the risk of offending Edward, who’s kindly provides answers on this site for the benefit of all, (and I would understand if he bans me) I would like to point out to Frank that the character ‘*’ is often used for the term A-shole, Moron is usually capitalized and sometimes Idiot.  My wife capitalizes ‘Butthead’ but I think these are all capitalized as those terms are proper nouns.  I also would like to think people have more than enough to do then ask questions when they clearly don’t want or need an answer, *.

On July 27, 2013 at 11:37pm
Edward wrote:

Jerry , you are the battery experter, are’t you? your comment about the battery is very professional!

Edward
zzrm316@163.com

On August 11, 2013 at 11:28pm
Lockie wrote:

Boris Kranjc wrote:
i have 5000mAh lipo 2 cell, 7,4 V battery. one cell was totally discharged and shows 0V. I suppose it cannot be fixed, only replaced?! Other is good.

Boris, I had the same problem with a 3S 2200mAh lipo, with one cell gone to 0V after accidently leaving a load on the battery overnight. I restored the battery (and cell) by small charges in NiMH mode on a Turnigy Accucell 6 charger until 3V/cell was reached and then used LiPo mode to charge normally.

On August 17, 2013 at 3:37pm
Magnus wrote:

Thanks for providing this useful and very thorough resource.
I have a question about charge termination by ‘peak voltage detection’ : The voltage is measured periodically to see if it has peaked. Is the measurement done while the charge current is flowing. Or is the charging paused in order to take the measurement?

On August 17, 2013 at 9:01pm
Jerry wrote:

Hello, Magnus.

Generally, the charge current is supplied by an external analog constant current source that is controlled by a microprocessor, either on or off at a minimum, though with extra circuitry, the constant current can be varied.

While charging under constant current load, the voltage is monitored continuously by a microprocessor ADC in most cases to be able to detect a 5mv or less drop per cell after either analog or algorithmic smoothing. To be clear, yes, the voltage is monitored while the charge current is applied.

Please note that this is only one way to terminate a charge.  I have found that delta Voltage is not quite as accurate as delta Temperature, and for Frank’s information, I capitalized the V and T to highlight the difference, and maybe to annoy him as well.

Lastly, the charger should have maximum temperature and charge voltage limit safeguards as well as a fail-safe timer.  Batteries catch fire. Period.  They should be taken very seriously while charging at anything higher than .1C.  Please refer to my earlier notes on the correct use of the character ‘C’ as it relates to charge rate.

All in fun,

Jerry,  with only the best regards for Eduard.

On August 18, 2013 at 5:26am
Magnus wrote:

Hi Jerry.
Many thanks for your quick response and further comments.
I’m planning to make an integrated charger using a BQ2002/F chip. It can sense a drop of 2.5 mV after peaking, and uses averaging of several voltage measurements.  But I think I’ll also need to add some analog smoothing to the signal as the charging current will be a bit rough from the step-down inductor.
Your comment about dT being more accurate than PVD is useful because BQ2002 only measures absolute temp and not rate of temp. Maybe I’ll look for a controller with this extra feature. Or I could write my own software, but it would be nice to get something ‘out of the box’.
Regards,  Magnus

On August 19, 2013 at 8:50pm
Jerry wrote:

Magnus,
I wrote my own software using an arduino board as there was a touch screen graphics ‘shield’ with Ethernet and SD card that I found useful to integrate. Granted it is overkill for a battery charger, I wanted all the flexibility to do it once and last forever.

Delta T takes a little more logic to detect, but the charts I made lead me to believe it is safer and more accurate than delta V for NiMH batteries. 

I highly recommend you take the approach of using your own microcontroller but it is more involved.

On October 3, 2013 at 10:37am
Alan wrote:

Hi Jerry.
As a school project we have to design the circuit of a charger of a NiMH 3.6V battery. It has to be charged by a USB only. Can I make it by only using the 5V source of the USB and an LM317? or do I have to vary the voltage too as the battery charges? How can I know when the battery is fully charged?

Best Regards

On October 6, 2013 at 6:21am
Jerry wrote:

Alan, I assume you can’t charge the three cells making the 3.6v pack individually?  I dont think there is high enough voltage at the USB port (without regenerating it higher) to charge a 3.6v pack.  Many of my NiMH single cells require 1.8v or higher for initial charge putting the absolute minimal requirement at 6v assuming a marginal voltage drop across the lm317 as well.

If you have a variable power supply, attach it to the battery with an ammeter inline as you increase the voltage to draw .05 times the capacity of the battery.  The voltage read at that point plus .6v, better plus 1.2v, will be the minimal amount needed.  Using .6 volts will require you to build a transistor based constant current source opposed to the lm317.

On October 11, 2013 at 6:57pm
Bill wrote:

This is an excellent site—I have learned a lot from reading it all.  I am still a little bit confused about my NiMH packs:
I have a smart charger but it doesn’t have a temp probe.
1.  I have a 4.8V 2000MAh powering the radio in my RC boat.  I run the model once a month or so.  I’m never really sure what percentage of the battery may have been used.  If I’m charging it at C/20 (100mA),  Is it OK to leave it charging for 24 hours?

2.  Another RC boat is powered by 6 cell 7.2 V NiMH packs.  One is 3700MAh, the other is 5000MAh.  My peak detecting charger has rates of 1, 2, and 4 amps.  I’ve been charging them at the 1 amp setting—but maybe I should be using a higher setting?

On October 12, 2013 at 10:43am
Jerry wrote:

Hello Bill, I will reply while waiting for Eduard.

1) Use any reliable thermometer against the pack after 24 hours to ensure the temperature doesn’t rise above 100 degrees F and you will be ok.  I question whether you are getting a full charge and I also believe you might be doing long term damage to the battery by charging at a trickle rate of 1/20.  My experience is that long term low current charging (below 1/15) might degrade battery performance.  If possible, I suggest you setup to charge at .1C for 14 hours.  As an aside, excuse me while I point out to Frank that the capital ‘C’ to designate Capacity was used correctly by both of us.

2) I suggest you charge batteries at that same rate as they are drained in most if not all cases. Never exceed the manufacturers specifications if

On October 12, 2013 at 8:09pm
Jerry wrote:

1) Use any reliable thermometer against the pack after 24 hours to ensure the temperature doesn’t rise above 100 degrees F and you will be ok.  I question whether you are getting a full charge and I also believe you might be doing long term damage to the battery by charging at a trickle rate of 1/20.  My experience is that long term low current charging (below 1/15) might degrade battery performance.  If possible, I suggest you setup to charge at .1C for 14 hours.  As an aside, excuse me while I point out to Frank that the capital ‘C’ to designate Capacity was used correctly by both of us.

2) I suggest you charge batteries at that same rate as they are drained in most if not all cases. Never exceed the manufacturers specifications if listed.  The only time I would charge at a higher rate than 1A is when time mattered.  Higher charge rates increase temperature which is detrimental in most cases.

On November 18, 2013 at 5:08pm
Larry Bartkowiak wrote:

Have a pro 95 and pro 62 radio shack scanner , can I use for a rechargeable battery a 2100mHa NiMH instead of the 1600 ? It comes with a 300mA AC charger ... Maybe I should use a separate battery charger with an automatic shut off , if they make one .  At what Rate would be the best to charge and what might be a battery charger to suggest , also anybody know of a good AA battery to consider , Thank you kindly for any response ...Larry   Larieb@aol.com

On November 18, 2013 at 10:58pm
Jerry wrote:

Larry,

Your scanner most likely came with a NiCD battery and the charger is probably just a 300ma power supply. I’ll bet the charge circuitry, if any, is in the scanner.  Actually the charge circuitry could be as simple as a resistor to drop the current to something like 160ma which is the recommended rate for a 1600mah battery when peak detection, temperature and other safeguards aren’t supplied.

If you can fit a 2100mah battery in there, and it looks like you can since you are inquiring about AA batteries, I don’t see any reason to not use it.  The charge circuitry in the scanner will still only supply the 160ma assuming it is limited to the supplied battery, so actually it will take longer to charge the new battery, something like 20 hours but you will have longer service life once charged.

I buy the rechargeable batteries you commonly find in electronics stores made by Duracel.  They are up to 2650mah capacity now and many times come with an inexpensive charger that works OK.  I don’t think they do all the fancy programmable charge detection algorithms you can find for more money, but they get the job done efficiently.  I would stay away from the 15 minute rechargeables, they never lasted for me as the charge rate was too high for the quality of the battery and typically they went thermal for me using their cheap charger.

There are a number of very good programmable chargers out there, maybe Ed can recommend his favorite, I built my own after playing around with others for many years.  I have stated in earlier posts that I have found the delta temperature / delta time charge detection to be more reliable with better peak capacity than the delta voltage type.  In any case, make sure you get a charger that has temperature sensing.  I would expect to pay around $60 or less for a decent charger and many could be had for less than $45.

Good luck

Jerry

On November 22, 2013 at 6:26am
Ed wrote:

Larry, just use the 2100mAh NiMH instead the 1600mAh, it will work well . and the 300mA AC charger will also work well with the 2100mAh ni-mh battery. Anyway, please contact with zzrm316@163.com for more detail infomation.

Edward

On November 22, 2013 at 4:35pm
Cameron wrote:

I want to charge a:
8.4 volt 3300 mAh Ni-MH rechargeable battery

I know very little about what V and mA charger I should buy for it.

On November 25, 2013 at 4:21am
Edward wrote:

please tell the charger seller the battery voltage and capacity , i think they will give you the right advice..  more question, please email to me zzrm316@163.com

On December 6, 2013 at 12:04pm
Alex Caplen wrote:

Hi there i am using the following battery and charger :
http://uk.rs-online.com/web/p/products/6117328/
http://cpc.farnell.com/1/1/14126-battery-nimh-12v-aa-2000mah-12v-aa-1600.html

It’s a pack made up of 10 AA NIMH batteries and is built into an amplifier which is left on charge until needed. Today i discovered a pack had overheated/leaked but i was under the imression from this charger that it would [revent this with safety timers etc. Could you please advise why this might have happened?

On December 14, 2013 at 7:16am
Ed wrote:

the charge current is high 16W/12V=1.33A . and i do not know how the safety timers work to prevent the battery from being overcharged. For more details please email to me zzrm316@163.com

On December 15, 2013 at 11:11am
Larry B. wrote:

Thank you for advice , always a pleasure to hear from somebody that has an idea of where I am coming from .... thank you !

On December 15, 2013 at 5:53pm
Ed wrote:

My pleasure to help you !! please be free to contact with me by email zzrm316@163.com

On March 3, 2014 at 6:39am
omar wrote:

i have rc battriy 7.2 v 2300m ,nimh and icharged it by imax b6 charger it will full in 30 min that very faster and battry not charged why? can i know the solution? by the way this battry is new i made it by my self in serial

On March 4, 2014 at 5:20am
Edward wrote:

Dear omar, would you please tell how do you set the imax b6 charger? in my opinion, if you do not set the right way to charge the battery, the battery will not be charged fully. As the ni-mh cell to say, please test the each cell voltage ,resistance and capacity if you can
please reply to me if you have any question about battery zzrm316@163.com   i am the rechargeable battery boy—-Edward

On March 23, 2014 at 3:25am
Paul wrote:

Ed
I want to charge a NiMi 7.2V 3200mAH pack of six D cells using my IMAX B6 but can’t work out what settings to use. I would like to charge them as quickly as possible, can you help please.

On March 23, 2014 at 4:23am
Ed wrote:

Dear Paul, please set the max voltage is 9V the charge current is 3.0A and the charge time is 60 minutes…notices!!  the battery must be fully discharged before charge.. more question please email to 13925239542@163.com

On April 1, 2014 at 9:45pm
Lex wrote:

Ed

My team and I are handling a research on rechargeable wireless sensor. We using six Sanyo HR-3UTGA 1.2V 1,900mAh batteries, while dividing them into 2 parallels with 3 batteries per parallel to power up the sensor. These sensors are then charge using two Solar Cell 5V 50mA (0.25W) connected in serial.

The problem we found is that some of the batteries (maybe few out of 6) will died off no matter we charge it under hot sun, indoor, or air-conditional room. Voltage of affected batteries will lies between 0.01V - 0.04V. These batteries still can be recharge until 1.4V, however, there will be higher chance for these batteries to break down again in future deployment.

Any suggestion for us to tackle the problem stated above? Are we overchaging the batteries and is there any solution to prevent it? Thank in advance.

On April 2, 2014 at 12:34am
Lex wrote:

Sorry for my mistake, the solar panels also in parallel form.

On April 2, 2014 at 3:37am
Edward wrote:

Lex , would yo please send me the photo showing how to connect the batterys and the solar cell??? in my opinion, you would better not connect the ni-mh battery in parallel form..  because they have different resistance and capacity.. my email is zzrm316@163.com   we advise you can choose the Lithium battery 3.7V 3800mah, only one Lithium battery will decrease the problem..

On April 21, 2014 at 9:01am
Mike Hulett wrote:

Hello!
I wanted to ask if the NMH batteries can cause static on a phone speaker if the battery levels are mismatched. (Fresh out of package, comes stock with a minimal charge.) I do testing for a phone company and I have noticed these batteries are shipped at a very low charge. If you bump or touch the batteries at this time, the phone speaker statics out. However, If the handset unit is charged for more than 2 hours, the static goes away. Any ideas?

On April 21, 2014 at 8:40pm
Edward wrote:

Mike Hulett ,I think the static came from the rub,  the ni-mh batteries are shipped at very low charge, that is for safty. more details please email to zzrm316@163.com Edward

On May 8, 2014 at 6:28am
Hari J wrote:

Hi, I had just purchased (8 May 2014)  a Sony CycleEnergy NimH 2500 mAH however the pack has the manufacturing date Oct 2013. Will this be an issue?

Overall it was well packed and store is one of the reputed retail chains in India. Just skeptical as I can’t afford another one and I do not have return options in India. Appreciate an answer.

Thanks.

On May 8, 2014 at 6:02pm
Edward wrote:

Sony battery have good quality, and it is the ready-to -use battery. I think it is not an issue, you can try to use the battery to check if they can work. and remember charge it when it can not work then try to use again .  email to zzrm316@163.com if you have more inquiry

On May 10, 2014 at 2:14am
Hari J wrote:

Thanks, Edward.

On May 26, 2014 at 7:30am
Martin wrote:

I always fully discharged my half used NiMH batteries before putting them into the slow charger. By doing so I hope I can accurately fully charged the batteries without overcharging it. The batteries are sanyo xxx 2700mAH and according to the charger manual, it took 12h to charge 2700mAh. Please help to tell me whether I am doing the correct method, or do you have any suggestion. Thanks!

On May 26, 2014 at 5:19pm
Edward wrote:

Dear Martin, Do not worry about the overcharge, the charger can stop to charge the battery if fully charged

On July 7, 2014 at 2:21am
M Dawson wrote:

Hi.. My garden solar string lights were not working so i ordered some new batteries for them ....Ni-Mh AA 600mah 1.2vbut they have come uncharged. My problem is buying a suitable charger for them. I have found a charger but don’t know wether it is compatible as the mah is considerably higher . I think it was 1200 mah but not too sure. Really dont want to waste any more money. Thanking you for your help !

On July 7, 2014 at 1:37pm
Jerry wrote:

what do the batteries look like, double A? AA?  If so, you can purchase up to 2650maH batteries in the hardware store with a charger.

Please reply with the standard battery number.

Jerry

On July 7, 2014 at 7:22pm
Edward wrote:

Dear M Dawson, I my opinion, the solar string light can charge the ni-mh AA battery ,do not they?