BU-804c: Acid Stratification and Surface Charge

Explore simple guidelines to prolong lead acid batteries by proper use.

Acid Stratification

The electrolyte of a stratified battery concentrates at the bottom, starving the upper half of the cell. Acid stratification occurs if the battery dwells at low charge (below 80 percent), never receives a full charge and has shallow discharges. Driving a car for short distances with power-robbing accessories engaged contributes to acid stratification because the alternator cannot always apply a saturated charge. Large luxury cars are especially prone to acid stratification. This is not a battery defect per se but is application related. Figure 1 illustrates a normal battery in which the acid is equally distributed from top to bottom.

Normal battery

Figure 1: Normal battery.

The acid is equally distributed from the top to the bottom of the battery, providing good overall performance.

Courtesy of Cadex

Figure 2 shows a stratified battery in which the acid concentration is light on top and heavy on the bottom. The light acid on top limits plate activation, promotes corrosion and reduces the performance, while the high acid concentration on the bottom makes the battery appear more charged than it is and artificially raises the open circuit voltage. The unequal charge across the plates reduces CCA (cold cranking amps), and starting the engine is sluggish.

Stratified battery

Figure 2: Stratified battery.

The acid concentration is light on top and heavy on the bottom. This raises the open circuit voltage and the battery appears fully charged. Excessive acid concentration induces sulfation on the lower half of the plates.

Courtesy of Cadex

Allowing the battery to rest for a few days, doing a shaking motion or tipping the battery on its side helps correct the problem. Applying an equalizing charge by raising the voltage of a 12-volt battery to 16 volts for 1–2 hours also helps by mixing the electrolyte through electrolysis. Avoid extending the topping charge beyond its recommended time. Topping charge is applied to maintain full charge and to prevent sulfation on lead acid batteries.

Acid stratification cannot always be avoided. During cold winter months, starter batteries of most passenger cars dwell at a 75 percent charge level. Knowing that motor idling and driving in gridlocked traffic does not sufficiently charge the battery; charge the battery occasionally with an external charger. If this is not practical, switch to an AGM battery.  AGM does not suffer from acid stratification and is less sensitive to sulfation if undercharged than the flooded version. AGM is a bit more expensive than the flooded version but the battery should last longer.

Surface Charge

Lead acid batteries are sluggish and cannot convert lead sulfate to lead and lead dioxide quickly during charge. This delayed action causes most of the charge activities to occur on the plate surfaces, resulting in an elevated state-of-charge (SoC) on the outside.

A battery with surface charge has a slightly elevated voltage and gives a false voltage-based SoC reading. To normalize the condition, switch on electrical loads to remove about 1 percent of the battery’s capacity or allow the battery to rest for a few hours. Turning on the headlights for a few minutes will do this. Surface charge is not a battery defect but a reversible condition.

Simple Guidelines for Extending Battery Life

Last updated 2017-11-15

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Comments (165)

On March 8, 2012 at 9:09pm
Eamon wrote:

I think that should be “use distilled or DEionized water”

On March 8, 2012 at 11:59pm
Bevan Paynter wrote:

If one has knowledge of water treatment technology as I do, one would know that rain water at about 20ppm will do- I use without adverse effects. As will melted ice water from fridge/freezer-even better. As comparison, distilled water is about 5ppm, de-ionized about same- tap water depending on source may have from 300- 2000 pm- TDS-(total dissolved solids or salts) -definitely harmful to batts & car /vehicle radiators! Also steam irons! A TDS meter measures level in sample- without one, simply use a multimeter on Ohms with probes dipped into sample- the higher the reading the better-i,e, infinity- drop a pinch of salt into sample & watch reading lower!

On March 27, 2012 at 10:36am
Bill the Fisherman with Deep Cycle Saddness wrote:

I added too much water to a lead acid battery and it performs poorly now.

Can i simply remove water and lower the level to just above the plates to restore battery performance ?

Or should remove water and add electrolyte solution ?

Is there a test kit for the proper electrolyte to water mixture ?

Is the specific gravity the result of the electrolyte and water mixture ?

Any info on test kits or fixing this self induced problem is greatly appreciated.

On March 27, 2012 at 11:23pm
Bevan Paynter wrote:

Much depends on type of batt & age of batt- on the face of it, adding slightly too much water should not matter much. The specific gravity of a batt is measured commonly by a hydrometer-cheaply available. The sg is highest when batt fully charged-ie all acid is in the electrolyte solution. I wonder why you had to add lots of water- thinking your batt may be worn out- or is your charging system over-charging? Even the best batts have a certain service life-ie no of charge-discharge, depth of discharge, sitting discharged- etc-etc-etc-all covered on this site. Fully charge batt- don,t overcharge. Measure sg. If low, could be sulfation, or you have lost acid by overfilling- spilling electrolyte. If so, you could try emptying electrolyte out of batt & refilling with new electrolyte- sg depending on type of batt.-eg starter batt=1.260- deep cycle- 1.220 @ 20’C. Look for crack or split in casing of batt- losing electrolyte. So there you are- if you can,t work it out from all the info on this site- we give up!.

On May 6, 2012 at 4:43pm
peter wrote:

Bevan, we have installed a lead-acid battery bank on a solar system 4 years ago. The system Voltage is 48 V and the batteries bank consist of 24 x 2 V batteries. Recently we noticed that some of the batteries have “cracked”. What could be the reason for this?

On May 6, 2012 at 11:54pm
Bevan Paynter wrote:

Peter- please say what “cracked” means- are the casings cracked & leaking electrolyte? Are the casings clear see thru polycarbonate? Are the casings bulging out-ie-swollen? If so- likely to be sulphation-also plates will have white coating if so. Sulphation is always caused by batts being undercharged & left that way. It is difficult to remove once there. I take it batt-ie each cell -has proper electrolyte level, o/c volts are ok, connector straps are making good contact? Unfortunately, RAPS once installed are usually ignored till trouble arises! The other thing all else being well is vibration or freezing temps, or even lightning strike!.

On May 10, 2012 at 10:17pm
Ron Johnson wrote:

What causes the white powder the accumulates on (usually) the negative electrode?  What can one do about it?

On May 11, 2012 at 11:36pm
Bevan Paynter wrote:

The white or grey coating on neg/pos terminals is caused by electrolyte vapour from inside batt condensing on metal ext parts- to stop, clean conn, refit securely, & apply a coating to ext metal conns- pet jelly, or hi-melt grease, or even an oil film. There are even commercial products that do the same thing-ie, insulate the terms/conn from the SO2 corrosion.

On July 5, 2012 at 10:49pm
Random guy with problems wrote:

I got 2 small lead acid batteries at a goodwill store, and neither works.  How can I tell what the problem is? I tried refilling one (12v, 3ah) with filtered and boiled water, but it did nothing.  What should I do, and if needed, where can I get electrolyte solution?

On August 19, 2012 at 1:59pm
Bill in DC wrote:

I have a little, home-made standby power system consisting of nothing more than a float charger, a flooded, lead acid deep cycle battery and an inverter.  It has served me well through our frequent power-outages here and saves me hauling out the generator except when it is really needed.  A few weeks back, I noticed the battery making cooking noises just connected to the float charger.  Sure enough, the water level had gotten pretty low, uncovering maybe 30% of the plates even though the battery has probably only had about 30 cycles on it in the last three years.  I refilled with distilled water and am hoping for the best (but assume I am probably stuffed and am going to have to replace the battery now).  When a battery is barely used like this and just sits on a float charger continuously, how often do you need to check the water level?  As I now know, the answer is more frequently than “NEVER”, but how often do you need to do this for a battery which is barely used?    Thanks much!

On September 20, 2012 at 11:21pm
mike foster wrote:

purchased distilled water from walmart for the batteries in my golf cart, the acid turned red and all my batteries went dead to marginal , so I figured the charger got them, picked up distilled water from walmart again, this time I topped off the two batteries in my
sailboat, now they are dead. checked out the fine print on the walmart bottle,  the water is filtered and fed ozone, by a variety of means.
So much for the distilled water,

On November 12, 2012 at 12:01pm
Ben Ho wrote:

I have several large deep-cycle lead acid batteries (not sealed) that I used to run my boat’s electric outboard. I left them in storage for three years, and now just discovered that the batteries are practically dry with no liquid visible. Is it possible to revive them by adding distilled water?

On December 27, 2012 at 3:55am
Munya Dread wrote:

Bevan Paynter, thanks mate for the fridge water tip, i guess its got fewer dissolved salts than tap water will give it a try

On January 10, 2013 at 10:26am
corey wrote:

Is there a home made recipe to treat sulfation?

also as i read above,iam now scared to use distilled water,whats up with that

On January 10, 2013 at 12:44pm
Bill in DC wrote:

I have to say, I got one of those BatteryMinder things with desulfation.  It actually works if you can be patient with it.  The batteries looked horrible when I let the water get too low.  There was terrible sulfation on the parts of the battery above the water line and I was sure I was stuffed.  Sure enough it wouldn’t take a charge to 13v after I put it back on the charger once I added distilled water.  But I pushed this maintenance mode which pulses the battery periodically and just let it sit on that.  At first it seemed to have no effect, but I just left it.  It took about 8 weeks or so, but eventually I could charge it again.  I haven’t stress-tested the battery and am sure it isn’t 100% of what it was, but when I look down in the holes the white sulfation is now entirely gone and the plates look clean all the way down.  And it seems to have good voltage and holds a charge effectively again.  I am no expert in this, but I would definitely try this before pitching a battery, even one with very bad looking sulfation.  I am sure there is a point where too much is gone and you can’t recover it, but it cleans up even plates that looked doomed in my experience.

On April 9, 2013 at 2:24pm
Faraz wrote:

can a pluser make prolonged the lead acid battery life,and avoid sulfation.

On May 6, 2013 at 9:06am
dave wrote:

what will happen if i remove the electrolyte of the lead acid battery, then after 4 months refill again. what will happen to the battery and the effect?

On May 8, 2013 at 6:38am
lenny wrote:

followed,let me try it hoping for the best

On May 11, 2013 at 4:21am
Rafiqul wrote:

I use 12v lead acid deep cycle battery for domestic power backup.  Unfortunately the battery goes dry up about 80% and battery doesn’t backup farther.  What I’ll do now?

On May 17, 2013 at 2:49am
wilford wrote:

why should an accumulator not be placed directly on the ground but on an insulator?

On June 4, 2013 at 9:20am
hind wrote:

i wonder if companies are still using the flooded batteries (lead -antimony)??? batteries and why don’t switch to agm and valve regulated lead acid battery .

On June 12, 2013 at 9:27pm
Bob wrote:

I often ask my self the same questions,  with all these advances in technologies yet a battery design from 1860’s is still being used . Why not revolutionize capacitance and retire lead acid.  I am told there are still too many benefits to lead acid battery’s that others aren’t able to match as of yet.

On June 18, 2013 at 2:26am
Faraz wrote:

can a electronic digital pluser make prolonged the lead acid battery life and avoid sulfation by supplying electrical spikes (votage) to the battery.

On July 17, 2013 at 5:01pm
Kaz wrote:

If we have a sealed battery, can we drill a small fill hole in it to let gas escape, check the water level and top it off as necessary, and then seal the hole?

On July 18, 2013 at 1:07am
hussain wrote:

how much time required to for lead acid batteries to connect with charger after filling electrolyte

On August 5, 2013 at 10:53am
Stennis wrote:

I have an application using flooded lead-acid batteries where the equipment will be used 6 months of the year (two days a week) and then stored for 6 months. I have seen some battery chargers that do a short “boil” every so many hours (e.g. 21 hours) to suppress acid stratification.  Is this necessary, useful?.  If not, what can be done to extend the calendar lifetime of such a battery system.

The battery system is composed of 36 high Ah automotive starter batteries.  The large number of batteries is required for short high peak power levels (>150 kW) but DoD during operation is only 3-5% followed by immediate recharge.  Battery life is believed to be calendar limited and is a significant operating cost

On August 5, 2013 at 11:08pm
Bevan Paynter wrote:

Without knowing exact details i am guessing. But the longest lasting start batts are neither over charged nor under charged- quality of make is a big factor.SLA type batts for starter use have far lower self discharge. This acid stratification thing is only a factor in flooded batts that are always stationary. DOD could be important, as buckled plates could result. Really- seems as if this application has not been really thought out!(IMHO).

On August 6, 2013 at 2:33pm
Stennis wrote:


The application is a battery-electric winch for use in launching sailplanes (gliders, not hang gliders).  The batteries supply the peak power (~150 kW) while a much lower power (~6 -10 kW) portable generator (or ac mains) replenishes the batteries through chargers under the control of a systems controller.  This system is analogous to a series hybrid electric vehicle.  The energy extracted during a launch is on the order of 1.2 kWh over a period of about 45 seconds with the peak power occurring very early in the launch and the power tapering down smoothly from there to a much lower level (~25 kW) by the end of the launch..  Peak launch frequency might be 6 to 10 per hour with maybe 25 launch cycles in a day pretty busy.  The excess capacity in the batteries (36 72 Ah 12V starter batteries would hold be about 30 kWh) can be used to buffer the generator during peak launch periods after which the generator could catch back up.  Otherwise, the batteries are being very shallow cycled. 

In many applications, the winch would only be used weekends and it would be stored during the week.  In northern climes, operations commonly cease for up to 6 months during the winter.  During this period the winch would be parked in a hangar and there would be no physical motion to stir the batteries.  During these storage periods the system controller can command the chargers (via CANbus) to do whatever would be best to maximize the calendar life of the batteries, e.g. boil briefly to stir reducing stratification and/or counter self-discharge.

For prototype development, the battery system employed is expected to be flooded lead-acid as it is the least costly option and does not require sophisticated battery management.  There are already a number of high risk elements in this development and a complicated battery system does not serve the goal of demonstrating the value of the fundamental approach over current IC engine driven winches.  Longer term, it is expected that these winches will employ LiFePo or some other such energy storage systems, e.g. ultracapacitors, that can provide the high power density necessary with greatly reduced weight and increased durability.

The question is, over extended storage periods what can be done via the chargers, under control of the system controllers (which can sense individual battery - not cell - voltages), to maximize the lifetime of the flooded lead-acid batteries in the prototype.  If periodically stirring the batteries would be valuable, for how long and how often should this be done.

[For an example of such a launch using a classic internal combustion engine winch see

http://www.youtube.com/watch?v=UOp_EsplxDM ]

On August 6, 2013 at 10:44pm
Bevan Paynter wrote:

Stennis- I would completely go away from battery launch- there is nothing like ic engines for quality, longevity, energy delivery density- & let us not forget the well being of the pilot/s- there is just too much to go wrong with batteries!.

On August 7, 2013 at 8:49am
Stennis wrote:


I cannot disagree with you more on the value of electrically driven winches but this is not the forum for that discussion. Cost effective electrical energy storage is currently one of the more difficult issues with this concept but I believe it can be addressed in the longer term.  That is why for prototype work I am planning to use lead-acid for its simplicity and capital cost effectiveness.  As I believe is stated elsewhere on the Battery University website, lead-acid is still the lowest cost per kW energy storage solution. If you would like to discuss the general concept of battery-electric winches further, we can figure out how to take that off line. I am always open to other views on this topic and would welcome the dialog.

But the question remains, what can be done via charging strategies during prolonged stationary storage to extend the lifetime of flooded lead-acid battery systems?  My application is just an example of a scenario that might have broader applicability.

On August 7, 2013 at 10:54pm
Bevan Paynter wrote:

Stennis- correct charging & load usage, avoiding sulphation, clean connections. As to de-layering of the mixed electrolyte- this is a subject that is by no means settled or even agreed upon that it happens. My experiments have shown that over-charging up to 16v certainly stirs up sediment from bottom of cell/s- mainly fine lead particles- now, whether it is thought that these particles are helpful to rest of cell/s/batt is up to you & everyone else to judge- i don’t think so!. Also avoid commercial additives promised to prolong life of batt- don’t work! What does work is a teaspoonful of mag sulphate, alum sulphate, & dbla(chelator) to each cell- takes about month to work(load batt heavily then immed recharge couple times). Batt seems as if new- did about year ago- still good on several diff sli batts(important- disconn batt from all loads- like immobilisers etc).

On August 8, 2013 at 1:24pm
Stennis wrote:


Thank you for your thoughts.  My read is that keeping the battery fully charged and making sure the charge is saturated is the key to long term storage.

You indicate that commercial additives don’t work but then describe your own mix that you say does.  Is there some technical basis for the chemical mix you describe?  If this mix works, why does someone not make a commercial mix similar to what you recommend?  What makes you believe existing commercial mixes are not similar to what you have recommended?

On August 8, 2013 at 10:54pm
Bevan Paynter wrote:

Stennis- no doubt there may be or will be(now!) mixes similiar- what I have tried & don’t work are anything mainly cadmium sulphate. (The majority). The formulas I describe have been used for maybe 100 years!. No mix will work where the batt has faulty cells-s/c or o/c- but where a little sulphation is present . The biggest trick is removing batt from vehicle after every run & fully charging it( the average vehicle never fully charges a batt- or in the case of taxis eg, overcharges batt- leading to short life in both cases.) the only way to charge batt is at constant voltage of 14v watching ammeter- when charge rate falls to almost zero batt is fully charged(modern chargers with micro processor control do same).

On August 11, 2013 at 9:13am
Dalton Hanks wrote:

I bought a new Roadtrek Etrek at the cost of $135000!  This CS Etrek is supposed to run AC , fridge and microwave(when needed) for 9 hrs.  The unit only gets 4 hours with 11000 BTU AC and Fridge on continually here in Florida.  My battery array is 8 six volt batteries and also a 240 watt solar panel for extra charging.  It also has a dual alternator as one is used for the battery array at 3500 watts on idle and 5500 watts going down the road.  Is that right?  Should it only get 4 hours or less when not plugged in?  Thanks Dalton

On August 11, 2013 at 11:14pm
Bevan Paynter wrote:

Sounds as if you have(had?) more money than sense! Batts are the big downfall in any alternative energy system- you all have to get used to economising on energy use!(ain’t free- like ac power seemed to be!)

On August 29, 2013 at 3:35pm
julius,chrizostom wrote:

you have helped me.thanks

On September 14, 2013 at 5:38pm
John Fetter wrote:

Stennis - Add nothing except water. To keep lead-acid in good condition in long storage, keep the batteries cool and give them a brief charge once a week using a timer. Observe the voltage rise during charge and set the timer to switch off at about 2.55 volts per cell.

On September 14, 2013 at 10:30pm
Stennis wrote:


Thank you.  That is along the lines I was considering.  Your interval of 1 week and charge to 2.25 V per cell is the kind of quantitative information I was looking for.  Any guidance on what C rate or range to do this periodic recharge to?

On September 15, 2013 at 12:15am
John Fetter wrote:

Stennis - The ideal current is the equivalent of an equalizing charge, for example C/20. My recommended charge termination potential is 2.55V. You might find from observation a lower voltage will work but 2.25V is too low. If you can, use intervals of two weeks.

On September 15, 2013 at 12:52am
Stennis wrote:


Sorry, 2.25 was a typo - I meant 2.55.  So your C/20 scheme does not intentionally ‘boil’ the electrolyte to reduce acid stratification? 

Just to be clear, the extended storage will likely be over the winter in an unheated storage unit.  In my local, eastern Washington, the highs should rarely be over 50 F with overnight temperatures commonly well below freezing.  Would that push out your recommended interval.

On September 15, 2013 at 5:55am
John Fetter wrote:

Stennis - Changing an already charged battery continuously at C/20 causes it to gas briskly. Charging an already charged battery that has been standing a couple of weeks and stopping at 2.55 volts “will catch its attention” in terms of gassing, that’s all. I believe the electrolyte will definitely not stratify. This method will not use much water. Cold helps to conserve charge.

On September 15, 2013 at 10:12am
Stennis wrote:


Thank you very much for the information.  I think I have what I need now.

On October 8, 2013 at 7:16pm
Don wrote:

I have four six volt batteries in series in my1995 RV purchased summer of 2012. I left them in the RV last winter ( which was fairly mild). They are house batteries. I notice now that the separators at tops of the cells are getting flaky and presume that this is sulfation or stratification starting to take place .I am somewhat surprised as I have a 2000 watt inverter and it is supposed to keep the batteries charged and I always use distilled water when topping them up. Can you give me a heads up on what might be the problem.
Many thanks

On October 8, 2013 at 11:28pm
Bevan Paynter wrote:

Don- “house batt” means deep- cycle? Disconnect each batt from others- measure term volts with dmm- all about 6v4? Next put em 1x1 on fully automatic “smart ” batt charger- @ full charge leave for week- term volts still up? If not is a s/c cell/s. If all are say 6v4 put each 1 on a high rate discharge test to see amps each puts out- if all about same means all are ok. Seperator “buckling” is usually nothing to worry about(at top)- it happens in all batts!. What is really useful is an impedance tester for batts- they are expensive to buy, but can be made cheaply. The principle is reading the acv across terms while pulsing a load- taken when new & periodically after, it says exactly the amount of aging in batt.

On October 9, 2013 at 5:49am
Don wrote:

Just want to say thank you for sending me a reply to my inquiry. .I much appreciate
your taking time to get back to me so soon.

On November 23, 2013 at 12:47am
kanthiraj wrote:

Dear Bevan,

I am electrical engineer, past 12 years in battery testing field especially in VRLA and Auto motive .Now we have problem with Flat plate batteries for invertor application.  In 12V/150Ah,1.250 Filling gravityand testes @27°C.  Initially it delivers in 400W test for more than 3hrs . But after 20 cycles it come down to 1:30 hrs due to gravity impact in all cells after recharge of 24 Hrs in 14.40V it raises 1.150 only how to solve the issue???

On November 24, 2013 at 11:37pm
Bevan Paynter wrote:

You engineer- me self taught! I would use ammeter in series with your 14.4 v charge- batt only fully charged when amp rate drops to say o.2 A. If no fault in batt plate assbly(s/c plates) may be plates absorbing acid thereby dropping sg. If happy batt is fully charged as above, adjust sg to get 1.260 @ 25’C- then see what happens in further discharge/recharge cycles. no doubt you are using refractometer to check sg?.

On January 16, 2014 at 7:40pm
Tom wrote:

Golf cart batteries, four 12v in series -  48v. — the famous rotten egg sulfur aroma has come calling.  It only visits when operating the cart - not noticeable when charging or when cart is fully charged and at rest. (Only seems to stink of sulfur when I get underway. 

I added some distilled water before the odor became really obvious.
Can’t find any damage / crack in battery case.   

Should be obvious that I am new to deep cycle batteries and elec vehicles.  Thanks for any consultations . . . 

On January 16, 2014 at 11:23pm
John Fetter wrote:

Tom - The smell is most likely from stibine, a gas that is given off by golf-cart and forklift batteries when they are excessively overcharged. Probably collects somewhere in the vehicle at the end of the charge when the batteries are gassing, gets blown out when you start driving the vehicle. Stibine is a compound of hydrogen and antimony. It becomes poisonous if you can smell it but carry on breathing it in anyway.
The positive plate grids contain, in addition to lead, a metal called antimony. It is used to make the plates more durable. Batteries normally give off a mild “bubbly” stink when they are charged. Caused by parts per billion of stibine. (Harmless.) This intensifies when the batteries are overcharged. (Harmful.)
Batteries do not give off sulfur.

On March 8, 2014 at 9:42am
CLaire wrote:

My 4 x 12v-100Ah VRLA Gel batteries rigged up to run my solar powered house. It has been working weel for 4 years but now the 12v lights go out after only 1 hour after dark. The batteries are not holding their charge. Will adding distilled water to the batteries fix them?

On March 24, 2014 at 9:54am
Charles Martel wrote:

Solid mass of crystals at outside base of battery.
I put a 12V on a trickle charger (on a metal table top); some days later I see a mass of sugar like gray crystals along the entire base of the battery, an inch high and an inch deep (!)
What’s the cause ? I assume electrolysis has some how pulled material from the table.

On May 27, 2014 at 11:04am
stuart wrote:

hi i got a yuasa battery for my sinnis qm 125 i had it like 9 months ago i filled it with water and left over acid from the pack i had as it was completely empty the caps got black on them and now i checked my battery today and its completely empty again what could be the problem any suggestions

On June 8, 2014 at 8:03am
siva wrote:

tall tubular battery i filled distilled battery water the ups exceed low battery when using time

On June 10, 2014 at 5:06pm
Frank wrote:

Can charging the batterie with low water level permanently damage it? If yes, why?
Thank you

On June 10, 2014 at 11:51pm
John Fetter wrote:

Frank - Your battery will have a low electrolyte level, not a low water level. The portions of the plates and separators that are submerged will be in acid that is more concentrated than normal and might suffer damage. The portions of the plates that are above the electrolyte will dry out and the negatives will become discharged.
You must add purified water ASAP. Do not fill to the maximum level but slightly below. Then charge the battery slowly and for many days. If the battery still works the electrolyte levels will slowly rise, initially the voltage will remain low and after several days the voltage will rise to somewhere in the region of 15.5 volts and the battery will be gassing. The gassing will mix the electrolyte and the water. If the voltage rises quickly and does not fall, buy a new battery. 

On June 11, 2014 at 7:37pm
David wrote:

Bevan Paynter
What is dbla(chelator) you refer to please?

On June 30, 2014 at 8:31pm
Utkarsh wrote:

Is it o.k to use the water from an ac unit to fill the battery?

On June 30, 2014 at 11:12pm
John Fetter wrote:

Utkarsh - I have used ac water in batteries many times. There may be dust in an ac that is used intermittently, which could be a problem, and algae in one that is used all the time.
Algae is actually beneficial to batteries.
Ask ten battery experts and they will all tell you not to use water with algae. My research group did, in golf-cart batteries, deliberately, to see what would happen. The algae increased their cycling life by roughly 50%.

On July 3, 2014 at 12:40am
mohit waghela wrote:

Beven, would you please tell me what is the reason of water turning black into solar tubular battery ? Should i remove complete water from it and filled with new distilled water ??
provide the relevent solution for this problem

On July 4, 2014 at 8:07pm
atif wrote:

Hi floks I just wanted to ask that I just purchased a new 12 volt 175 amps flooded battery for my ups as agm batteries are not available here in pakistan it has been a month since I haven’t checked the battery today I checked the caps of the battery and I noticed black layer on the inside of all caps its not completely black but cloudy plz can u guy tell me if my battery is fine or what.

On July 4, 2014 at 11:29pm
John Fetter wrote:

atif - A flooded type is better. It can last about twice as long as AGM. The black stuff is harmless. It is predominantly carbon, mixed with other materials, that are put into the plates by the manufacturers. There may be some oil as well, from the separators. Traces of these materials are typically given off by the plates and separators during charging. These materials float on the acid electrolyte and the gassing from charging causes them to splash onto the caps. If I did NOT see this in a battery I would become worried.

On July 10, 2014 at 3:18pm
Josh G wrote:

What would happen if you used Chilled Water that has been treated with chemical from a closed loop instead city with was filtered? The wet cell battery is a duo cell battery.

On July 15, 2014 at 7:26am
RICK T wrote:

I believe that my batteries froze this past winter. When I put them on charge all batteries started expelling liquid in small quantities. Since then my battery capacity is dramatically reduced. what can I do.

On July 29, 2014 at 1:45am
tonykid wrote:

Question. As I open my solar battery the electrolyte is dried there is no sign of water. pls can I refill it with distilled water or with the acid water

On July 29, 2014 at 2:04am
John Fetter wrote:

tonykid - You can fill with distilled water. Then charge slowly for a long time. There is a high likelihood you will not be able to recover the batteries due to the low electrolyte, which causes plate damage.

On July 29, 2014 at 6:31am
tonykid wrote:

But sir I saw people taking there battery to refilling service center. and after it work fine

On July 29, 2014 at 7:35am
John Fetter wrote:

tonykid - I suggest you do the same thing.

On August 21, 2014 at 3:09am
sunil wrote:

any one can give a solution for our doubts, the battery voltage is 12 and the spgr is 1.250, when discharged the battery with 400 watts bulb, the back up is just 20 minutes.
the battery is just 2 yrs old

pls advice

On September 1, 2014 at 8:52am
Sarima wrote:

Hi, my battery’s capacity has drastically reduced after I added battery water. It’s perfomance has been half of that I used to get before adding water.
The battery was bought in August 2011.
What can I do to restore it??

On September 1, 2014 at 9:38am
John Fetter wrote:

Sarima - I suspect you may have allowed the electrolyte level to fall far enough to expose big areas at the top of the plates to the air. These areas will have become totally discharged and might be damaged. They are now taking all the charge and giving very little back. You must give the battery a very long, slow charge to attempt to restore these areas.

On September 9, 2014 at 9:42am
Royce wrote:

I have a golf cart with six 6 volt lead acid batteries, NOT maintenance-free. Five of them are over 3 years old, the sixth one was replaced this year. They are all boiling the liquid out and will not hold a charge long enough to power the cart. I think they are all toast, even the newest one. Am I correct? What might be the cause of this boiling?

On September 10, 2014 at 5:02am
Jeroen van Oosten wrote:

I’m having a weird problem with a battery where the electrolyte level keeps dropping.

It’s a small motorcycle battery, 14Ah, wet cell with caps to fill. It’s fairly new, 18 months old, but not used much (a ride every few weeks). I removed it from my motorcycle 2 months ago because it couldn’t start the engine. I noticed fluid level in two cells was way too low. So I topped it up with distilled water, gave it a quick charge and let it rest because I had other things to do.

Yesterday I was trying to charge it slowly, using a lab bench power supply. I first checked all the cells and noticed a few where the plates were not submerged (though still wet and above the minimum level), so I gave them a few drops of water and started charging. I set the voltage to precisely 2.30 V per cell, and it was charging with 0.63A for a few hours (less than C/20). I measured the voltage and amperage each hour and by the time I got to bed (7 hours later) the current had dropped slightly; the battery was producing some bubbles. I then disconnected the power supply. Everything looked okay.

But this morning, the fluid level in one cell had dropped considerably! The other cells are okay, just one cell is10% below the minimum level on the battery (I can’t rememember if it was one of the ‘dry’ cells when I removed the battery from my motorcycle). I did not top it up yesterday. Open circuit voltage of the battery was 12.20V.

- Is it normal for a battery to bubble, even at a low voltage and slow charge?
- What could cause the electrolyt level to drop considerably, even after the charger is disconnected?
- Do you think this battery is still salvagable?


On September 11, 2014 at 12:13am
John Fetter wrote:

Royce - Your batteries are being overcharged. Something is wrong with your charger.

Jeroen - 1. The rapidly falling electrolyte levels indicate over charging. The voltage readings indicate undercharging. One of these is not correct. You are in the best position to check.  OR
          2. An impurity has somehow been put into your battery electrolyte that is causing an increase in the rate of self discharge.

On September 17, 2014 at 11:29am
Jeroen van Oosten wrote:

John - Thanks for your answer. It is indeed very weird, the battery shows signs of both over- and undercharge. I am also inclining towards an impurity or other manufacturing problem. Either way, this battery is toast.

On September 18, 2014 at 5:10am
Shekhar Rastogi wrote:

Dear Sir,
I purchased a lead acid tubular battery 150 ah for my domestic UPS (900 VA). I found the fully charged battery as my UPS showed operated 150 watt load just for 3 hours. But as per calculation the battery should have worked for at least 8 hours with this load. I called the technician and he told the specific gravity was low just 1.150 and that a specific charger may be used to increase sg. The battery is only two months old. My first question—-What back up time should I expect from the battery for 200 watts load and second question—-Would the sg of the battery would remain normal after being charged by the charger as stated by the technician?

On September 19, 2014 at 10:10pm
Shahrukh sheikh wrote:

My ups charges the battery @ of 30A12v. The battery is lead acid nonsealed battery of 100A. Now the problem is this that the charge of battery continuously decreases when the ups stops after full charging. Then ups again starts charging the battery without any usage. Please can you help me what should I do in this situation.

On September 20, 2014 at 12:32am
John Fetter wrote:

Shekhar - A battery in the situation you describe, with an SG of 1.150, is for all intents and purposes fully discharged and needs to be charged. It is possible your charger is not working properly.

Shahrukh - A lead-acid battery that is first fully charged, then simply left standing, will discharge slowly, on its own. This can take six months, a year. The UPS will try to counter this by occasionally giving the battery a brief charge. You have not provided information about the time or current when the UPS starts again. I have given you an interpretation. If I owned a UPS and it did not do this, I would get worried - not the other way around.

On September 20, 2014 at 1:38am
Shekhar Rastogi wrote:

Thanx a lot, John. You are right, the battery was fully discharged. It worked for very little time. Eventually, the dealer has changed the battery. He has given me a new one on its place. It is working good.
Thanx once more.

On November 1, 2014 at 2:32pm
frank wrote:

Wow, a lot of confusion and stuff ups here. 

40 years ago our fathers knew how to maintain the simple lead acid batteries in their cars but the actual charging mechanism was in the car alternator and fixed.  No one played with any other systems like we do today, it was simple. 

Today many people want to take batteries out of their native devices and tinker with them, build their own electronic systems basically.  But unless you have spent many many hours researching and setting up your charging system, do not expect anything but failure.

Batteries are complex electro-chemical devices, they are not like a bucket you simply fill with water.  Voltages and currents and time periods must be kept within specific boundries or you will destroy these sensitive devices.  AGM and gel cells only complicate the issue.  So either get a professional to set it up for you of do your homework, lots of it!

On November 2, 2014 at 6:26am
John Fetter wrote:

frank - I believe you are right about batteries being complex electrochemical devices. Batteries made from the purest lead that has been processed into high quality positive and high quality negative plates, the purest acid and provided with the purest refill water throughout their service do not last very long. Add the right impurities in exactly the right concentration and they just go on and on working. Can you suggest why?

On November 12, 2014 at 6:07pm
Conrad wrote:

about lead -acid batteries.  In golf carts: some 36 volt with 6- six volt batteries; some 48 volt with six 8 volt batteries, or 4- eight volt batteries.. In all cases this battery of batteries are charged overnight with a single charger.  I would like to charge my trolling motor and boat batteries with a single battery charger…in my basement for overwinter storage.  Can this be done with a simple parallel wire hookup (using 6 ga. stranded wire)? ...or are diodes et al. necessary in the wiring scheme?
    Also, regarding older (6-7 yrs old), deep-cycle batteries and restoration efforts.  Years ago, someone told me , and I never tried it, that adding an aspirin to each cell, would aid in rejuvenating the battery cells. I may have been gotcha’d…but has anyone tried this remedy with any positive results

On November 16, 2014 at 3:20am
Ashwajeet Singh wrote:

When i opened my bike’s battery after two years ( it seemed dischard all the time) i found the electrolyte was solid at the bottom i topped the battery with distilled water from a closed container but i still gave performance as before. What to do?

On January 1, 2015 at 10:15pm
keith wrote:

Strange one…
The battery is a 232 amp hr deep cycle (6 volt) and it has been doing an odd thing.

I check the electrolyte at the end of a charge/absorb cycle and one cells volume is low, the other is almost over flowing. I even out the electrolyte among the cells. It charges during the next day. I check the electrolyte and one is really low and the other is over flowing.
Is it possible for one cell to be “leaking” into the other?


On January 3, 2015 at 5:48am
ashish wrote:

Hi,after changing battery water my inverter is not charging the battery.what should I do now.plz help

On February 6, 2015 at 9:42am
Larry wrote:

I just recently installed an off grid Solar Array. Wanting to keep my batteries in the 20% DOD range I determined that I would apply a charging system external to the solar charging during a few night hours.  At first I was just waiting until the voltage on the system dropped to 80%. But then it dawned on me that if the chemical action created by charging leads to shorter battery life, then I might be doing harm or shortening the life of the batteries by applying charge only after discharge as opposed to applying the charger to maintain a charged state until a a few hours after dark. So now I have the secondary charger take over right at sunset and maintain the charge latter into the night. This creates only on chemical reversal per 24 hours instead of two. Does this seem like sound reasoning?

On February 22, 2015 at 2:53am
Edward P wrote:

Interesting in this discussion that no one has mentioned Peukert’s Exponent in their solar grid calculations. This is why batteries do not last as long under load as you would think.

On February 22, 2015 at 5:13am
John Fetter wrote:

Edward - Everyone knows the higher the current draw, the lower the available ampere-hours. Perhaps not everyone knows this by its formal name, Peukert’s Exponent.
Peukert predicts battery performance under ideal conditions. Batteries in real life tend to deviate from this ideal for many reasons. This is what people are attempting to discuss on these pages.

On March 26, 2015 at 11:41pm
Steve wrote:

My 12v battery I use for my boat is pushing out water out the terminals after I put it on a new 5amp trickle charger I just bought for about four hours and also topped up the water levels before charging as they were low. For the past three days water is slowly coming out one or two terminals that is actually closed. What caused this to happen and how can I fix this problem? Your advise is much appreciated.

On April 22, 2015 at 6:12am
Praneeth wrote:

Sir I have bought 4 deep cycles batteries for my car but as my car goes on a dump,the batteries are shaking and water is moving up and down. If this problem prevails what happens to the batteries?

On May 1, 2015 at 7:27am
Ankur wrote:

My deep cycle battery lost all its fluid inside.. It didn’t run dry on its own.. the fluid leaked out on the floor top opening when it tipped off one day. So now should i fill my battery with distilled water or sulfuric acid electrolyte solution?? And should i fill the fluid to the top?? Any suggestion would be helpful.

On June 30, 2015 at 6:12pm
Mike wrote:

I recently purchased a pallet of large size 8d deep cycle batteries from an auction. They are new, but have dates on them between 5-6 years old, They were stored covered in a trailor but out in arizona with some high summer temps. The water levels are all still above the plates and voltage readings are on average 4-6 volts (12v batteries) my friend tried charging 2 of them without luck, they wouldn’t appear to budge on a charge…..  any tips to try and rescue these before I scrap em out? Seems like a shame but even being new they obviously were not stored properly… Thanks!

On July 9, 2015 at 8:39pm
Ron wrote:

I have two 6v Deka deep cycle batteries that will each charge to 6.45 and then settle to to 6.35.  When checking SG, I discover each cell is only approx 1.2 ...a low reading that suggests recharge to raise the SG higher.  After a recharge of both batteries, I get the same results.  Does this mean I need to get them equalized? 
I have been concerned that my converter in my RV trailer is bad and that my batteries are suffering because of it.  I will probably replace the converter before placing the two batteries back in the trailer. 
My main concern is that my batteries can get back to a good SG reading of 1.265.  If not, then is replacement suggested?

On July 10, 2015 at 12:08am
John Fetter wrote:

Ron - A voltage of 6.45 will put no charge whatsoever into a 6V deep cycle battery. You must use a charger that can charge until the battery voltage rises to at least 7.6 to get a deep cycle battery up to 100% state of charge.

On August 23, 2015 at 8:12pm
SHIRO wrote:

if low level of fluid then you can add distilled/ionized water on the battery. After adding charge the battery 4-8 hours depending on the CCA of the Battery. Then installed the battery on the vehicle and idle the engine for 1hr. Test the battery, if the result is lower than the stnd CCA then The Voltage is 12.69 then you need to replace the battery.

On August 24, 2015 at 2:03pm
Mark wrote:

Excellent post. This explained an unusual battery situation we experienced where (after a key fob had been left in the vehicle overnight) the battery experienced a discharged as the car continued to ‘poll’ for the presence of a key (this is an electronically started Mazda 3). The net effect seemed to be that stratification took place (which hid itself in tests after we jumped the car and then had the local auto store run diagnostics on it). The auto store found no fault (voltage looked normal as well as cranking amps) ; but then a few days later the car failed to start again < so the car lights were turned on, removing any surface charge, and then the diagnostics were run again > THIS time the test failed, revealing that the CCA were not (as we thought earlier) 400, but instead, only 120. Now it all makes sense. Thanks BatteryUniversity 8-)

On September 21, 2015 at 8:17am
Fred from Florida wrote:

I have a new (2 mos old) battery, 780 CA at 32 degrees and 625 CCAs.  My symptoms are 1) it looses it’s charge overnight to below 12.6v so will not start, and 2) it is discharging water/acid out of each vent hole located on top edges of caps.  I’ve checked several times for parasitic draws, always getting a “0.00” reading.  Note: at one time I did have a few parasitic draws but remedied by grounding directly to a cooper bus bar connected to neg battery post.  What could be the cause for the loss of charge and water discharge?  Thanks

On October 27, 2015 at 6:18am
Stuart Walsh wrote:

Excellent information! My BMW 320D is 13 years old with the original battery. This morning the engine failed to start. I took the battery out and put it on a charger but the charger’s “charge” light was dim and then went out after a few minutes. I thought the battery must need replacing.
BUT!!! I read this article about acid concentration so I tipped the battery onto one side then the other over and over for about 2 minutes then attached the charge leads and it is now charging correctly.
Perhaps many apparently dead batteries simply need to be shook up to redistribute the acid concentration.

On January 9, 2016 at 6:29pm
Bill wrote:

Dear Bevan,
I have a 4890 watt PV system.
I have 6 banks of 4 L-16, 401 AH batteries.
In the summer my sg is 13+. In the winter it is 11.75.
Is this of concern, and if so what can I do. All I have read is that I should keep it up.
My generator comes on when V is 21.8, for 4 min.
My generator shuts off when V is 28.8 for 10 min.
My sunlight hours are Dec 21, 9hr, Mar 21,12hr, Jun 21, 15hr, Sep 21, 12hr.

Thank you, Bill


On January 9, 2016 at 7:44pm
Bill wrote:

Can anyone advise,

I have a 4890 watt PV system.
I have 6 banks of 4 L-16, 401 AH batteries.
In the summer my sg is 13+. In the winter it is 11.75.
Is this of concern, and if so what can I do. All I have read is that I should keep it up.
My generator comes on when V is 21.8, for 4 min.
My generator shuts off when V is 28.8 for 10 min.
My sunlight hours are Dec 21, 9hr, Mar 21,12hr, Jun 21, 15hr, Sep 21, 12hr.

Thank you, Bill

On January 13, 2016 at 7:59pm
Asish Chessam wrote:

Battery is still filled full quantity of acid but not getting charged and it is draining fast in use.Now I have emptied all the acid by pouring it out and washed many times with water but it is still sour taste. What should I do ? Should I fill water or H2SO4.

On January 23, 2016 at 9:13am
Engr Asad wrote:

Plz tell me that can we add distilled water to the battery in charging status or we should to disconnect the battery from system or string for adding distilled water???

On January 23, 2016 at 9:22am
John Fetter wrote:

Engr - Simply wait until the battery is gassing, is nearly 100% charged, just before you switch off the charger, is probably the best time to water.

On February 8, 2016 at 11:41pm
Warren wrote:

My friend has a 24v deep cycle 12 batterybank system that has been left on high bulk for a week at around 30v and now the batteries gas even when disconnected, the SG is reasonable on most cells. What would be the cause of the new gassing levels? They gas all the time even when at a lower voltage, are the plates really clean now so present a larger surface area or would there be sulfation across some of the cells? The water keel never went below the plates.

On February 9, 2016 at 12:21am
John Fetter wrote:

Warren - The overcharging caused some of the antimony that is in the positive grids to be leached out and to be electroplated onto the fully charged lead metal active material of the negative plates. The antimony deposits on protruding portions of the lead active material, thereby setting up short circuited electrochemical cells with the underlying lead of the negative plates. These will initially gas profusely. The gassing will eventually slow down after some more deep cycling and the antimony will end up buried inside the negative active material.

On February 25, 2016 at 11:32am
Brian Johnston wrote:

You mention ionized water to batts, what I got for batts id DEIONIZED.
Which would correct?

On April 19, 2016 at 5:01am
Abdul wrote:

I want to know that when we adding or top up the distilled water in to the in service lead acid batteries installed for the Ups system , does the battery acid will out and spill outside.bcz normally when water is added to the acid containinig inside the small container, there is burning and spillage .

On April 19, 2016 at 5:49am
John Fetter wrote:

Abdul - Add the water only if the electrolyte level is low and only when the battery has been fully charged. Put in just enough to bring the level to the correct level. Do not put water in a battery that is discharged and do not fill to the top.

On April 30, 2016 at 8:11am
G. Strauch wrote:

I have a 6v batter for my tractor. This spring I checked the water levels and put it on the charger, and it seemed to be charging properly, but the next day the error light on the charger was on. I disconnected the charger, and opened the caps, two of the wells looked fine, but under the cap of the third was a solid white mass that looked like a plug of styrofoam. What’s should my next move be? Get a new battery?

On May 4, 2016 at 12:51pm
Pam wrote:

Guess I’ll go turn on the charger and start with battery bank!

On May 28, 2016 at 5:11am
Tina wrote:

I’ve been reading some of your advise.  I have a motorcycle battery with some levels levels normal some are low.  I’m reading to refill with distilled water but to charge it first then fill? Or fill then charge?

On June 7, 2016 at 7:13am
James wrote:

Do you only remove the surface charge every time you test the battery or after recharging it?

On June 11, 2016 at 2:23pm
Anita Weiss wrote:

to Tina
fill to just cover the plates first
charge, long slow charge C10 rate with a lab power supply till 13.6 or 13.8V
sometimes it may take more than 24 hours, especially if the battery is sulfated
then fill to halfway between min and max marks on your battery

the chargers at autoparts stores are at best SO-SO for automobile and truck batteries
not recommended for motorcycle


On June 16, 2016 at 6:47am
John Addy wrote:

I have 6-8 V Wetcell batteries in my golf cart. I don’t think it’s running as strong as it used to so I did check the water and it was low. I filled them back up in a sense recharge them but I still think I’m lacking some power, any ideas

On June 16, 2016 at 3:20pm
John Fetter wrote:

John - If you say you recharged in a sense, it suggests you did not do a proper recharge. You absolutely must do a full recharge plus equalizing charge. You need to overcharge at a low current for half a day.

On June 17, 2016 at 1:51pm
hasan wrote:

I am facing problem with my car . few days ago I drove the car going well after some miles suddenly stopped. I made self after long self again start I was happened about when ever I drove. after last few day I observed that when I self to start the car self take in low battery cark cark cark low low and battery power off. main time I start again with my friend car’ battery attached cable wire with friend cars battery and good start. I drive well when next morning I again start car same problem I again faced such as make self crank carank low again low and battery power again off. some one told me battery water checked . I observed some water was low in each cell. I fill with filter water . but problem was same. some one told me complete water take out from battery and again fill with electrical water I do and complete again refill with electrical water . plz note that out of 6 cell one cell completely fully . I can not take of water due to not understand how. after I start car I was happy car start but after 5 minute again stopped. a try to again start and make self but again battery down after some self. plz advised me

On June 27, 2016 at 10:29am
Mike wrote:

I recently built an off grid house with a 4500 W PV system based on a 48V. HUP battery bank. It appears that the batteries were chronically undercharged for at least a year due to a faulty battery monitor system and low charge rate settings This was identifies when a proper hydrometer was finally used and low s.g. in the 1.220 range was noted. The monitoring process has been identified and corrected. The charge settings have been raised to the highest recommendations from the manufacturer. I know that there was damage done based on s.g.readings .  I can only get s.g. up to around 1.255 with aggressive charging and equalization.  I have been running a pulse charger for 6 months in hopes of preventing further sulfation.  Any thoughts on how to further salvage these batteries? Any chance of getting the s.g. back to 1.265? This is my only power source and I really want to maximize battery life and capacity.  Thanks for your help.

On June 29, 2016 at 4:23am
robin rickhi wrote:

hello I have 48v bank of rolls batteries been charged by solar, the guy who installed it two years ago came and serviced the system and added more electrolyte mixed with distilled water in the automatic battery watering system. however I realize that the batteries are holding the charge overnight since. can there be too much electrolyte in the batteries and can this be remedied..


On July 17, 2016 at 4:47pm
Edward Howard wrote:


On July 23, 2016 at 7:17pm
Anita Weiss wrote:

unfortunately, yes

the fact that the batteries are sealed, does not mean they do not need maintenance
it is just that it is no longer accessible!

some newer batteries are such that I have to drill holes in the cover!

On July 23, 2016 at 7:30pm
Anita Weiss wrote:

to James
there is no simple test for (lead acid) batteries
they are rated CA, CCA, and RC sometimes Ah is specified
these are complex and expensive tests, and doing-it wears the battery

the simplest is RC, it consists of a 25Amps load, and measure how many minutes it takes to reach 10.5V
compare this to the stated value to estimate the wear level

a new battery would probably be ruined after doing this test 10 to 15 times

On July 25, 2016 at 7:09am
luca rossini wrote:

I use 48V traction open lead-acid batteries for a solar self consumption system (i.e. always connected to charge/discharge).
am looking for a way to reduce wtaer loss in order to reduce the number of times we need to access and top up with distilled water.
anything wrong with leaving the cells completely open, and add a hose system with a big reservoir, keeping them full at all time?
thanks for the insights.


On July 25, 2016 at 3:50pm
John Fetter wrote:

luca - Your idea won’t work. You can fit industrial battery filler caps. NEVER try reducing water consumption. You will inevitably reduce the life of the battery.

On July 26, 2016 at 12:08am
luca rossini wrote:

Thanks John!
We have indeed industrial battery filler caps.
More than reducing consumption, my bad, I expressed myself wrongly, I would like to make an automatic system for refilling, with a big 100Litres reservoir lasting for say 30+ refills.

is there anything existing out there, for this purpose, avoiding to come and manually refill distilled wtaer every 3 days?

thank you.

On July 26, 2016 at 9:02am
John Fetter wrote:

Luca - Use a simple garden hose irrigation timer. I have never heard of watering every three days. Are you cooking the batteries?

On July 26, 2016 at 9:57am
Mike wrote:

If you need to refill your batteries every three days I would be checking your charge settings.  That seems pretty excessive and would suggest that you are over charging the system.

On July 28, 2016 at 6:40am
Phil wrote:

I have a bank of 3 x 110 Ahr leisure batteries on a boat charged by solar to fully charged every day. They are cycled daily but only to 10 to 20% max. Their usable capacity I have recently noticed is now only about 20% or less. The rested voltage is about 12.8 at sunset. The SG is showing fully charged. A heavy discharge tester is showing good when fully charged however, once 10 to 20% has been removed the discharge tester cause the voltage to collapse to about 2v at a current of 10A. The voltage rapidly recovers to full voltage 12.7.  I have never had to add water and have given the occasional equalisation charge. What do you think is going on? I have currently removed them and they are all 3 sat happily around 12.75 volts.

On July 30, 2016 at 11:46am
Scott wrote:

What is dbla(chelator)?

On August 2, 2016 at 7:30am
Anita wrote:

without knowing exactly your system, one can only speculate
! check that the electrolyte level is above the plates (that the plates were not exposed to air)
2 that the charge voltage is 13.6 to 13.8V. 12.8 is too low
3 get a laboratory power supply, set-it at 13.8V (current limit to 3 to 5Amps)
after 2 to 3 days the current should be stable at some value (somewhere between 0.001 and 0.3A)
at that point rock the batteries about the longitudinal axis, ±45º (just so it does not spill)
if the current increases more than about twice the stable value before rocking
then the batteries may be stratified

On August 2, 2016 at 2:14pm
Phil wrote:

Thank you for your reply. To clarify:
The electrolyte has always been well above the plates and hasn’t needed to be topped up. It is also reading fully charged on a hydrometer.

The 12.8 reading is the rested voltage after charging, not the charging voltage.

The charging voltage is 14.4v dropping to a float level of 13.8v after a period of absorption charging.

The acid is not stratified as the battery is given an occasional equalisation charge.

The current at float charge is around 0.2 of an amp.

The batteries are charged daily.

I have actually just taken one of them and after removing a few amp hours was able to short it with a current of about 40A falling rapidly to less than one. The voltage is now not recovering although the hydrometer on all cells is reading fully charged.

It’s quite confusing as it can’t be sulphated as indicated by hydrometer and the fact that in normal use they are never taken below 80% charged. I assume it isn’t positive grid corrosion in 2 years as the electrolyte hasn’t had to be topped up at all and they are ordinary flooded lead acid with no hydro caps or cleverness.

On August 5, 2016 at 11:23pm
David wrote:

Which is the right procedure,add water to acid or acid to water in a lead acid cells?

On August 10, 2016 at 2:20pm
Greg wrote:

I was taught initially that when maintencevon any battery was being performed and that whenever ( distilled ) water was being added, to always afterwards perform a ” equalize ” charge to chemically equalize it which will get the battery up to proper charge.

It doesn’t look like it from reading these posts though

On September 6, 2016 at 5:45am
Rabbit wrote:

Stennis, are you still looking for correct method to store batteries over long periods of inactivity.

Did you choose your batteries according to me which should be SLI type (automotive batteries or start stop type) for high discharge current for short periods - if so did you select Antimony (Sb) only chemistry on positive plate or calcium plus antimony conventionally written as Ca only for the positive plate (or may be you chose Se). Ca positive plate has lower discharge rate, but oxidizes faster and does not have typical deep discharge capability like Sb only. But Ca gasses lesser, self discharges lesser (even lesser than Se). If you chose Ca then I am not sure but may be do not subject the batteries to such high charge as 15-16V for 12V battery or the positive plate will oxidize faster. Antimony can with stand high voltage charging, but as they also gas higher, they will also gas accordingly and lose water and will need to be topped up therefore. If Ca battery is chosen try to watch out if they are not able to maintian 50% charge then they may be replaced for your critical application - unless there are redundant batteries in the system in the event of lower power provided by a few. - I say this as Ca battery should not be discharged down to 20% etc. (actually you should see the manufacturer data sheet on charging and storing recommendations). Sb only positive plate batteries have more depth of discharge capability at the cost of heavy maintenance, so can be used even when older till they are able to supply the current you need! Ca may have more inertia or sluggish when they get older. That is when they reach below 50% capabilities. Also ensure while storage the battery terminals do not have a discharge load. (even if less). Of course you may be already using or knowing that relays can provide non mechanical battery disconnection.

Another interesting thing is that, for people having vast array of batteries to manage, sometimes there is a non corrodable form of float and piping system used to automatically top up. I do not know how useful that is, but if it not possible to check water level then that system could have helped. Of course distilled water shall freeze at water freezing point and will only flow into pipes when melted. and freezed water in pipes may break them!

Ensures battery do not get any mechanical shocks - especially as they start growing older. positive Plate can shed oxide paste that way.

Batteries have limited life - whether used or not because of self discharge/corrosion -  they are consumables and you should replace battery when they show signs of weakness. Some manufacturers put thicker lead oxide paste to make them last much beyond the expected battery life which may be the warranty period - but that may not be as predictable.

On October 6, 2016 at 7:12am
Michael Campbell wrote:

I am new to solar power. I installed 6 12 volt deep cycle batteries last year. They appeared to be sealed and “maintenance free”. When they no longer held a charge I investigated and saw that they were not maintenance free. A tear off label concealed filling ports. Anyway the batteries were all bone dry. I added distilled water and charged them with grid power and a good quality charger for a week. When returned the batteries to the system they worked for a couple days and died again. Are the batteries repairable or are they toast? At least I learned I am supposed to check the electrolyte levels every month.

On October 6, 2016 at 10:18am
John Fetter wrote:

Michael - It appears from your description that you may be using ordinary car batteries on solar duty. If you deep cycled car batteries more than 100 cycles they will likely be finished. The major golf-cart battery manufacturers make a special type of battery for solar. These batteries have one inch quarter-turn vent caps. They need to be watered. Fit a single point filler system. Connect via PVC tube to a handy PE 5 liter container. Simply punch a small hole, force in the tube, the hole self-seals. To water, lift the container, unscrew the cap to let in the air, wait a few minutes, screw down the cap, bring the container down to just below the filler caps. Only do this after an equalizing charge.

On October 6, 2016 at 12:14pm
Michael Campbell wrote:

John that is disappointing. I was under the impression that the deep cycle marine batteries would last longer. Anyway I did order 4 of those 130 lb 6 volt batteries to replace the ones I have. I plan to monitor them carefully to ensure they do not fall below 50% and the water level is always above the plates. But I was wondering if there is a way to reverse the damage to the old batteries I caused by letting them run dry so I could use the old batteries for another project like a small solar system lighting the latrine etc.

On October 6, 2016 at 12:39pm
Phil wrote:

Michael, sadly your batteries are probably not salvageable. It would be worth checking the settings on your solar controller as, even with flooded batteries, they shouldn’t dry out in a year if the settings are correct. I see no indication that they are starter batteries as you state they are ‘deep cycle’ this may mean leisure batteries in which case you need to avoid taking below 50% and prfereably 75% to get a decent cycle life out of them.

On October 6, 2016 at 4:21pm
Michael Campbell wrote:

Yes Phil. Also in my excitement to get into solar I added too many batteries for the solar array to charge, especially iunder 5 feet of snow and two eeeks of cloud in a row. The old ones dragged down the new ones. I added a fridge which drew down everything to like 20% which I now understand is bad for the life of the bank.

On November 13, 2016 at 2:08am
Phares wrote:

thanx for the comments I have been highly equiped with valuable knowledge.

On December 3, 2016 at 4:19pm
Farah Ali Shah wrote:

Hi Dear,
I am farah I want to ask you a little quition about my lead acid battery which is I am buying 5 month ago actually I am a single mother & doing two jobs in a day so my all day going in the working so I can’t give a little time to home accessories for look after them In this cause a few days ago I saw my home ups battery is going In a very low water’s condition means not in much dryer condition just a little bit water after all this I am putting the dstle-water now my ups battery is well but it’s going in the warmer condition it’s see like heater after few hours continuously charging. When it’s going warm condition I am stop the charging & used the battery power for lights which are energy saver light of 25 watts or volts which are used for 7 or 8 hours at battery power then giving ups low power alarm & then I am again charge the ups. It’s my problem which make me so much worried.  I can’t afford any expense in these because I am a single handed lady who look after the two families all the depended member so please do some thing for us.
How can my ups battery becomes normal again
In our region the load shedding is a very big problems so why the ups is big a helper of us in the giving electricity
I know all of you have been understand my condition & now let do some thing for us I am great full to all of you guys.

On February 10, 2017 at 2:23pm
Anita wrote:

to Michael Campbell
Some batteries may appear bone dry, but they are not!
They are starved electrolyte
The whole thing is that battery sellers will say anything to make a sales!
All these technologies AGM, GEL starved electrolyte…are about shipping lead acid batteries via air transport. Air transport operators are worried of batteries exploding or catching fire…

Depending where you live and your actual application
In my area there is a metal recycler (a large place) that have tons of batteries. They buy batteries at 25¢ and sell at about 37¢ a pound
Now, these are scrap batteries I am talking about
In the pile, there are many lift truck batteries, (a large pile of lift truck batteries) most are useless, because too big and heavy, but have lots of juice per $
Automobile, small/large truck, bus, train batteries, some have a good deal of life for UPS type application. They may fail to start the locomotive engine at -30º, but will keep the lights ON for a good while. Per $, they will outperform anything new! Some are so dirty, they are not worth looking at.
You have to pick and test from the piles. I find that telephone (central office) batteries have very little wear because they have to be replaced periodically due to legislative measures. They are the least abundant, automobile are the most abundant. The telephone office batteries are always very clean, well maintained (the best)
Some truck (rented moving truck) the batteries just need to be charged and watered, and they can go a long while. Rented trucks for moving get started very often, very short drive…battery won’t start vehicle
Operators don’t have time or ability, they replace the battery and get the vehicle back on business.

these suggestions are to help you achieve low cost engineering

On February 10, 2017 at 3:32pm
John Fetter wrote:

Farah - Put distilled or purified water into your batteries to replace the water lost by charging and by the heat. Not too much, just enough. Do this once a week.

Anita - Excellent advice. Quite a high percentage of batteries that are scrapped are still in very good condition.

On March 14, 2017 at 1:48am
Jenna Alexos wrote:

I have just purchased a bottle of non-acid electrolyte water at my local garage.  The lady said it could be used in my battery for top up.  All the rest of the writing is in thai, so I cannot read.  Is the non-acid water suitable for my battery.

On April 2, 2017 at 10:21pm
Pete wrote:

Good day,
I purchased a coloumeter and wanted to check capacity of my car battery. I fully charged it, then discharged with 1/10 current of the battery capacity (70Ah EFB type).
While discharging, I had to leave the battery unattended and when I returned, the battery was already over discharged to 1,7V (unluckily, I didn’t have any circuit to cut the load at 10.5V. I quickly disconnected the load and the voltage started to recover. At 4V I connected battery charger (CTEK MSX-5) and let it charged. When I opened the vents I noticed acid been stratified (muddy). Do you think that even short 2hrs deep discharge could cause this? Thank you

On April 26, 2017 at 3:43am
A.Sami wrote:

A newly purchased UPS 200AH lead acid battery is found to have weak electrolyte ie 1220 instead of 1250. What effect will it have on its overall performance and ultimate life.
How can we make it 1250.Thanks
Kind Regards

On April 26, 2017 at 11:36am
Pete wrote:

It will last much longer, but the capacity will slightly be decreased.

On April 27, 2017 at 10:02pm
satya sahu wrote:

I have a one year old 220 Ah Luminous Tubular battery with Microtek-860 EB Inverter along with solar panel 450 watt and one solar management unit of 12/24 volt with 10/20 amp. Since last one month water level of battery is lowing frequently. So I repeatedly filling distilled water on 4/5 days interval.  Plz suggest, what is the ground and what is the remedy.  With regards,

On May 1, 2017 at 11:56am
Pete wrote:

Satya: Your battery is most likely overcharged and often boiling. That would explain loss of water.

On May 2, 2017 at 5:24am
Phil wrote:

Satay, I assume you have a 12v system with the one 12v battery?  A 450W panel is an unusual size, is it actually two panels? With an MPPT controller you have a potential charge current of around 30A at 12v so your 10A regulator is not upto the job. As it is dual voltage are you sure it hasn’t been set on 24v?  Some regulators, if you connect panels before batteries, will set themselves up as 24v and then overcharge your batteries. I would advise measuring battery voltage while it is being charged in the afternoon so is hopefully full, the voltage should not be over about 14.7v and, if it has gone into float, should be about 13.7v excessive water use of all the cells indicates over charging.

On May 15, 2017 at 12:07am
shikhar budha wrote:

i have 5 years old hollandia battery of hp 12-100D 100 AH now a days its constant voltage is low and it gives no longer duration power when i looked after opening cap of battery there is no any liquid, what should i do for its maintanicesss

On May 15, 2017 at 3:55pm
Anita wrote:

To shikhar budha

just add water, it must be distilled water, nothing else
as it will cause damage

On June 3, 2017 at 12:28am
Samuel wrote:

Luminous Bettary 150Ah
Firstly, i filled acid full in bettary.
And I had already used in 3 years. Now the bettary is easyly down and no strong power / so I want to refill acid/ distilled water but I do not know which kinds of things should i fill.
please kindly tell me what should i fill in bettary. (Eg. acid or distilled water)


On July 20, 2017 at 4:45am
AANYA wrote:


On July 30, 2017 at 5:24am
Anita wrote:

To AAnya
just add water, the acid does not evaporate
and it is important to use distilled water

any mineral salts will electroplate within the battery and this surface is forever unusable

it may be wise to add water maybe once a month as opposed to wait till the battery is dried

On September 30, 2017 at 7:39am
Mane wrote:

Hi, i have one problem. My alternator was charging my battery too high. So, i believe that I have a serious lack of water in my battery. It’s a sealed battery, so I can’t check water level. Can high OCV be indicator of low water also? I measured 3 last days. It was 12,8-12,9. Always 24h after drive. I’m thinking of braking the top of the battery just to add water. What so you think?

On October 3, 2017 at 4:35pm
Anita wrote:

To Mane
What prompts you to think the voltage is too high?
what is the voltage when idle, no lights or min load?

some batteries are difficult to open. They open like an egg!
That is, the plastic parts cannot be closed (glued back together) one solution is to drill holes in the top cover.
However I would not recommend unless you know how that particular battery is built

On October 4, 2017 at 12:57pm
Mane wrote:

Well, 12,9V is too high for me.Maybe I’m wrong, but as I know, 12,6~12,7 is voltage for full charged battery. And I remember it was like that before. So, now, when I measure 12,8~12,9, it gives me some thoughts.

When idle is 14,4V, but 2 weeks ago when I measured, it was 15,5V~16V with throttle. So, I fixed regulator, and now it’s ok.

I thought about drilling, found some videos, but I’m not sure if every battery is same that way. That’s why I think it would be safer and easier to just open it.

On October 7, 2017 at 11:04am
Mane wrote:

I decided to open the battery anyway. On my surprise, every cell had water above the plates. Some less, some very high. Specific gravity was also very high, about 1,31. Since I already bought electrolyte, I decided to change it. I spill the old one, and put the new one. 3 liters were more than enough for 600A battery. I expected 6. So, I degraded new electrolyte to 1,28 SG It was 1,33 in bottle. The strangest thing is that when I measured SG of new electrolyte in battery, it was lower than before. Other strange thing is that 2 cells had little lower SG than others. How is that possible when I put same electrolyte in cells. I spilled it and measured it again. And it was 1,28 again. Can anyone explain me this phenomenon cause I don’t get it…

On January 13, 2018 at 12:42pm
Alfonso wrote:

Great website. My congratulations.

I have been receiving signals that my lead-acid battery car is down. I have a voltage gage connected to the cigar lighter of the car and the average reading is 12,02 volts, 11,90 some times. After using the car for a while, and measuring the battery voltage in rest, the reading highest was 12,20 volts. I thought the battery was down but I had no idea it was something serious. Also the car has had problems to start in the morning with the voltages specified above.

Last thursday my battery car didn’t start the engine after making two stops. This is what happened:

I drove to one place 600 meters away, turn off the car, made an errand, restarted the car, I drove to another place, to 1700 meters away, turn off the car, restarted it again and drove to another place to 600 meters away, turned it off and after that it didn’t start.

Then one taxy driver helped me out (God bless him). We took out my battery he connected to his car alternator, since we didn’t have auxilary cables, and we charged for about 5-10 minutes. We had to tilt the battery almost 60 degrees forward to reach the cables of his car since the battery cables of his car were short.
Then we puted my battery back to my car. I read the voltage, and for my surprise was 12.60 volts, after only 5-10 minutes of charge. Then I could easily turned on the car.

My first questions are:

1) As you can see I always drive a lot of times short distances, most of the time with my A/C on and sometimes with my cd player on.  I lve in a small town. Is it possible that my battery is just stratified?

2) I have never reached 12,60 volts after using my car a lot. How could reached that voltage after only 5-10 minutes of charge? When we tilted the batery did we homogeneize the acid in the battery?

After that I panic and went immeadiately to a Battery service. I requested a Battery charge and a clean of the battery cable terminals. After half an hour we puted the battery back in the car, and the battery didn’t give a stable voltage. 8 voltage, 9 volts, sometimes 10, and the car didn’t start. We started the car with the help of another battery but when it is on, the lighs inside blink, and the voltage is not stable.

Then the service guy opened the battery, added distiled water, some of the vases were half empty, and we recharged for another half hour. After that, the car started and I could get home, the voltage was still not stable, but not as low as before. I got home, keeped the car on for a while, but the lights keeped blinking. I turned it off, tried to start it again, but the voltage was about 11.54 volts. After 24 hours the battery has lost most of his carge. I measured it and it was about 9 volts.

My last questions are:

3) Is this battery lost? What happened when I charged it?

4) If it is not lost, and it is only stratified: can I get it back with a long charge of 2 hours? What voltage should I use for this charge?

The battery has been being used for 3 years, 7 months old. I have the invoice with me.

I am determined to buy a new one but I need to get where the batteries are sold. I am in Venezuela, a country devastated by a dictatorship, and I have to travel 40 kms. to a major city to buy a new battery and carry the old one to the sales place. I would like to go with my car using the old battery.

¿Can I recovery it for this long trip?

Now I have the battery resting on one side, to see if the acid homogeneizes previous to attempt a new long- charge

Sorry for the long post, but I think you are a real experts about this topic. Thanks in advance.



On January 31, 2018 at 9:55pm
Karl wrote:

Hi!  I have a car battery that i put on my trickle charger until it reaches 100% 12.6v.  Soon after taking it off the charger it will stop dropping, all the way down to about 10.6.
I opened up the lid and measured each cell and a few of them were about 1.7v.
I got battery acid from autozone and refilled them and the readings were around 12.1v total.
I let it charge for a couple hours at about 1 amp current until the charger said it was full, i checked the voltage and it was 12.6 steady so i waited for 2hrs, it still said it was 12.6.  So i put it in the car, started it and it was great.  Turned it off, waited about 3 hours, now it’s back at 10.3v (10.6 unplugged from car). 
I plugged it back in, started the car and drove home about 15 minutes…
At home i took the battery out and let it sit for about 45 minutes, the voltage was dropping but steady now at 11.2v.  Any thoughts?  Do you think something is draining it while my car is idle?

I’m going to charge it up to full again and let it sit for another few hours and see what happens.

Thank you for your expertise!

On March 17, 2018 at 5:57am
Nafees wrote:

I have purchased an (AGS 200) lead acid battery about 12 days ago. But its performance looked poor. I took it to the seller who is an Engineer s well as UPS dealer. He told that he would fox the problem. But I doubt if my battery would work properly. Its under guarenty for a period of three months. Should I claim for its replacement? Please respond.

On March 22, 2018 at 8:02am
Bob wrote:

After 3 months sitting, my golf cart batteries in Florida, I am told they are dry and completely dead. Why do they go dry and am I being scammed? The dealer put new ones in only three years ago. What is the best way to keep them charged over a 3 month period, trickle charger, solar charger, or What? Please help !

On December 2, 2018 at 10:27am
Don wrote:

I have a question regarding batteries on a isuzu truck
These batteries are the original batteries, they have lasted about 12 years.
The batteries are sealed. I have been unable to find a way to check the electrolytic level.
Connections are absolutely clean ( taken apart, everything wire brushed to the bare shiny metal, all connections are tight, lighted grease)
DMM reads 12.53 Volts. Measured each separately and disconnect from each other same reading. Put load on and the reading is 10.40 Volts
It can only crank a couple times, before it stops.
What may be the reason for this? I have searched quite a few sites, but can’t come up with a conclusive answer. Is this what may be called a surface charge?
Can anything be done to recover these batteries?

On February 11, 2019 at 8:46am
John Montgomery wrote:

I just purchased a neglected sailboat that has been converted to electric propulsion. I have 8 6v US 125xc batteries. Voltage level indicates 53.3v for the DC buss. I found 3 of the batteries with the plates exposed. I added distilled water to cover the plates and buttoned everything up.

I have a low end 6v 12v battery load tester and hydrometer. How can I best predict the health of the batteries?

FYI batteries are marked, by hand, 10/14. I’m assuming that’s install date.

On March 2, 2019 at 5:36pm
JanS wrote:

Switching from flooded lead-acid to AGM is no a great idea. There is charging profile in cars alternator circuits, that doesn´t fit with AGM needs! AGMs are overcharged if there is no modification to the cars charging circuit. AGMs need lower trickle/floating charge voltage, especially if operated in hot environment. Overcharging leads to (mostly) drying out the water from electrolyte thus decreasing its capacity and life expectancy dramatically. This servers knows it well (https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm), I justi missed such a caveat in this particular article…

On March 5, 2019 at 9:44am
Mr Tin Tin wrote:

Hi there!
I think I have a problem. Bought some used sealed lead acid batteries of 12V 7aH. So I thought lets fill them up before charging. So went to a batterie store asked with what to fill them.
They gave me a water with Sulphuric Acid(37%) solution. Filled al the batteries but now I’m reading here(and checking on youtube) to just fill them with distilled water. What should I do?
And I’m charging the batteries just with a solar charger(because that why i got them) but do I need to buy a better charger for the first good charge? (sorry for bad english)