Lead Acid Battery Care and How to Restore Them

Introduction: Lead Acid Battery Care and How to Restore Them

About: I like to improve myself and things I find :) Learning new things every day is next to impossible but I still try - only a working brain can work. I have no special sector to cover, electronics, electrical s...

Today I came across a very misleading Instructable promoting a
commercial website and giving totally wrong infos - so let's try to make it better!

Winter is coming and your car battery is already a bit on weak side?
Or you had the battery stored unused for a long time?
In those and some other cases your mechanic will suggest to buy a new battery.
And let's face it: For a small, standard car battery it might be the best option anyway as they are quite cheap.
But what if the battery if bigger, like for a 4WD or a truck?
Worst case would be a shed full of big batteries for your solar system if you are off the grid...

In cases where a new battery would be a financial problem or the battery is physically fine apart from old age you might have science on your side :)

If you are interest keep reading :)

Step 1: What Causes a Lead Acid Battery to Age and Loose Power?

If you trust science then charging and discharging a lead acid battery goes like this:
During the charging PbO2 is formed on the positive plates.
During the discharge it forms back to lead as a reduction process.
Problem with this I don't trust science without questioning when it comes to the real world application LOL

The reason manufacturers state a life time of around 3 years of usage is because in our real world the battery "ages".
A perfect charge and discharge cycle throughout the life of a battery basically never happens.
This is why some good solar charge controllers are so expensive: They try the best to keep the battery healthy.
Still the battery won't last more than maybe 4 years or 5 if the climate is very nice throughout the year.
And of course only if you always keep the destilled water at hand to top up the battery cells.
Before you ask: No, the following won't work on a dead or badly abused battery.

The aging happens because of the formation of sulfate on the positive lead plates.
This not only partially isolates the plate surface but also reduces the capability of PbO2 reduction.
A physically fit but lightly ages battery shows a white buildup on the plates if you have enough space to see it.
This is the lead oxide (PbO2) and the more that remains the lower the capacity of the battery will be.
If this buildup is too much it cuses bulging of the plates but also the destruction of the lead plate itself.
Holes or other areas where only PbO2 remains won't "heal" again as the base is lost.
Even if the oxide is reduced back the lead it won't be a flat plate anymore but something that looks like a mountain range.

Step 2: Keep Your New Battery Fit and Healthy for Many Years!

A new battery is easier to prepare than trying to restore a battery that is already deemed to be past the due date, so we start here.

When you get a new battery it comes pre-charged these days.
This means the shop only fills the sulphuric acid in and you are good to go.
As said sulphate is what we don't wont see on our plates!
Many chemical reactions are affected by impurites, catalysts or simply a different temperature.
The same is true for the phosphate build up in our batteries.

If you add about 5ml of phosphoric acid per cell to your battery mix the phosphate process will be greatly reduced and some cases totally blocked for several years.
Ok, too complicated?
Phosphoric acid can be obtained in many shops for different purposes, even Coke has it in the mix.
For me the cheapest option was rust remover from the hardware store.
Although in these concentrations the acid is quite harmless to your skin I strongly recommend using nitrile gloves or to wash the exposed skin as soon as possible.
Wearing googles or using a face shield is always a good idea as you only have two eyes!
Use a syringe, dripper or measuring cap to get 5ml of phosphoric acid.
Add to the battery cell and repeat until all cells are done.
So called maintenance free batteries still loose water and can be topped up - usually it is only a pressed in plastic strip covering the caps on the cells.

You new battery is now ready for a prolonged life :)
To keep it that way I recommend another 2 - 2.5ml of phosphoric acid per cell every 12 months together with the top up of destilled water.

Step 3: Restoring Older Batteries

If the battery is cheap get a new one!
If the battery was badly abused over the years it might not work!
If the battery plates are already bulged, you have build up on the bottom or even plates with a short a new battery is required.

What works great for a new battery also helps your oldtimer.
Only downside is that it takes some time and might not always work as good as you hoped.
As before you start by adding about 5ml of phosphoric acid per cell - for bigger ones like truck and 4WD batteries use 7.5 - 10ml.
Top up with destilled water - no tap water, no rain water, no de-mineralised water.
Now you want a good battery charger capable of automatic functions like these new trickle chargers that would keep an unused battery fully charged while still bein able to charge empty ones in a relative short time.
Old style, transformer based chargers might require close monitoring from your side to prevent gassing (the acid in the cell bubbles like an open bottle of your favourtie soda drink...
Once the phosphoric acid is added and the cells topped up you want to charge the battery for about 3 full days, a week if only charge during the day or night due to monitoring the process.

Here is what actually happens:
During the charge the lead oxide (PbO2) is reduced back to lead.
The presence of our phosphoric acid now also reduces the phosphate on the lead plates.
Over time more and more of the PbO2 will now turn back to lead.
If after three days of charging there is no visible change in PbO2 reduction - the white stuff on the plates, it could mean the battery is too damaged to benefit.
In a car a battery like this would have struggled to start the engine for some weeks already.
If you do see a reduction of PbO2 but no further reduction two days later it might help to add another 2.5ml of phosphoric acid per cell and to continue the charging for another 3 days.
Now you should see a definate difference to the look of the plates compared to the start.
That means you battery is good to go if the follwing points are all true:
a) The charger is no longer pumping amps into the battery - if the battery still draws more than 500mA it is either not fully charged or you might have too much build up of either PbO2 or sludge at the bottom of the battery.
b) The acid still looks clear in the cells - if it is cloudy, brownish or you see a lot of tiny things floating around it means the battery was too damaged to be fixed this way.
c) If you disconnect the charger and let the battery rest it should still show 12V or slightly more when you measure the next day - a self discharge here indicates either damaged plates, damaged isolation between the plates or a build up of sludge at the bottom of the battery, again bad luck.

Words of warning for the charging:
As I don't know the state of your battery it is your job to keep yourself safe here!
Don't charge the battery inside, have it outside in a plastic box or container to the stuff is contained if things go wrong - you don't want sulfuric acid spilled in your home, garage or garden!
Unregulated or old style chargers are often strong enough to deliver more than 5A for the charging.
Especially at the start a weak battery will draw a lot of power from the charger and the battery can produce a lot of hydrogen gas in the process.
You want the cells to be able to release this gas so don't seal you maintenance free battery back up for the charging.
A working battery is usually no problem here, but more abuse and age can mean a short is produced during the charging.
A strong charger with no protection will be able to overheat the battery to the point where the plastic melts, the acid boils over or if the pressure can't escape the battery explodes like a water bomb.
All the above should not be a problem if you use common sense:
If the battery was totally useless before already, looks like a piece of crap or had the plates already sitting dry for a cm or more than you should only try if the new battery would really stretch the budget too much and use the mentioned precausions.

Step 4: Ok, What About My Extra Large 2V Solar Batteries??

I know that replacing these beasts is a cost factor to be considered if you rely on them.
And it is not like you could simply drive the next store and pick up a few tons of batteries either.

For obvious reasons it is best to act in time, meaning you either prepare new batteries or add the phosphoric acid before the batteries show signs of aging.

Good batteries allow for a visual inspection of the plates, some have a "window" others come in a clear plastic housing, which I really prefer as they are the best in terms of visual control.
Since some companies don't see the need for such user friendly designs to save a few bucks you might have to buy a little inspection camera.
They are cheap enough these days to be justified for the needs, just make sure it is fully a fully waterproof cam head.
I still suggest to add a nice layer of acrylic varnish or clear coat except onto the lens itself of course.
For obvious reasons you also want to rinse it after use to remove any possible acid residue.

Your biggest problem is finding the right amount of phosphoric acid to add and the best way to allow for prolonged charging cycles if the batteries already show the brownish phosphate layer.
The service book or at least the booklet to the batteries should state how much acid is required per battery.
I recommend 2.5ml of phosphoric acid per 100ml of battery acid as a start or for new batteries.
No further thing required apart from the usual checks as instructed by your manual.
For older batteries I still recommend to start with just 2.5ml of phosphoric acid per 100ml of battery acid unless you already have a clearly visible phosphate layer or even white sopts on your plates that won't fully disappear even after a few days of charging.
These bad cases should get 3.5ml per 100ml for the initial dose of phosphoric acid.
Once that is done it is best to have the charging cycles set so the batteries won't go below 85% of the capacity during use and to allow for a few hours every day where the batteries can be "floating".
Meaning the batteries are full and the charge controller only sustains the charge.
After about 2 weeks you should see a clear improvement on your battery plates unless of course you always have to drain the batteries on a daily base - here it will take about a month until you see first improvements.
If your plates look fit and healthy again within 6 weeks of the initial treatment you are good to go.
In case there are still white spots or brownish areas left add another 2.5ml of phosporic acid per 100ml of battery acid and keep monitoring.
It also helps here to have a charge controller that is capable to be set for a slight overcharge for a few days.
Either by an increase in the charging voltage or as simple as per menu function in the service functions.
In either case I recommend to stick to longer floating times if possible and to keep monitoring the batteries for 3 more weeks.
I say that because some older systems struggle to provide a true floating time unless really nothing is connected that uses power.
Here the inverter is always fed through the batteries as a buffer for the solar cells instead of converting the solar input directly.
Getting a true and 100% charge in these systems can be impossible with a load running.

Only severe cases would not recover with the above volumes of phosphoric acid added.
Although a little too much won't really hurt the battery I do not recommend it unless:
a) the battery was quite old or weak to start and then still only if:
b) there was a clear reduction in PbO2 / phoshate but it slowed down and fully stopped.
In the above problem the phosphoric acid was used up by the reaction.
If nothing at all happend visually adding more won't help as I would problems with the charging cycles first.

The restored battery should not only perform better but also allow for usage times closer to their original state, in some case even better.
Caring for it is now the only thing you need and apart from following the booklet you also check for the formation of phosphate or PbO2.
A check after 6 months and then monthly should be good enough until you find the right balance.
Solar system are usually far better here than car batteries and if you are lucky there will be no more lead oxide or phosphate build up.
Simply create a checklist for the build up test like this:
During the usual check and water top up you pick one battery for smaller systems and two for bigger ones to check for lead oxide and phosphate.
Mark these on your list and select different ones for the next check.
This way you circle through the batteries and won't miss anything.
In the rare case of another build up simply follow the previous instructions and add some phosphoric acid again.

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    11 Discussions


    Question 9 months ago on Step 4

    I have a 24 string of 2 volt batteries. They’re pushing over 20 years. I used them in the past 7 years for solar, they’re getting tired. I would like to refurbish/rejuvenate them. Before using phosphoric acid should I filter the debris from the bottom, having a translucent container I can see?


    Answer 9 months ago

    I did some maintenance on battery backup systems in my early years.
    Mostly 1.2m high cells with a square of 15x25cm.
    Ultra high Amps...

    We used a dirt cheap aquarium pump of the external kind to filter the cells once a year.
    For the filter media it was just cut to size pot scouring pads for the first layers and then one final layer of cotton wool.
    Had all the aquarium standard stuff like a tap on the inlet and outlet, nothing fancy for acid use.
    Still it worked fine for all the years I did the job.
    Acid stayed in the pump.
    Dowside for you is that you would have to fill the pump and hoses first with a acid solution matching what you have in your cells.
    If you don't want to make it a regular thing:
    Get one of these cheap fuel transfer kits.
    You know, a bit of hose and the push ball to get the stuff moving for 5 bucks.
    Suck all debris from the bottom of the cells into a suitable container.
    Try to be careful so you won't cause too much movement with the hose that could distrurb fine debris.
    And if in doubt use a thin PVC pipe so you won't scratch over the lead plates!!!
    Once all debris is collected get a coffee filter you no longer need and filter paper and let gravity filter out the crap.
    Use the filtered acid to top up your cells again.
    Please use proper PPE, especially for the face and eyes.
    Battery acid is not too bad on the skin but wash all asap if you got in contact!

    Before you add phosphoric acid try to check the plates.
    If they are dark black, show holes or flakes then they might just be too old.
    A fluffy layer of greyish-white stuff that turns to a cloud of dust in the acid with a gently touch might mean your batteries overheated for a prolonged time.
    In this case you should watch out for salts flocking out after you added the phosphoric acid.
    A build up of whitish stuff on the bottom of the cells a few days later means you need to get it out before it reaches the plates.
    It also means your improvements won't be really great as the plates where to damaged.
    Assuming the plates are fine start with a small amount of acid per cell first.
    Preferably added when the batteries are quite low so when you start the charging the bubbles will mix the acids properly.
    Try not to add any acid when it is unknown when you charge the batteries, always try to add right before starting to charge.
    Monitor the levels and conditions over a week and check how much the performance improves.
    Note for every day what you voltemeters, amp meters and acid tester reads.
    After 3 or four days of normal use you should see first improvements.
    Keep monitoring until there is no further improvement, then again add a small amount of phosphoric acid to the cells and continue to monitor.
    Once there is no further improvement or your plates show a nicelight brown color when fully charged the batteries should be back to whatever performance level they are capable considering their age.
    I would not expect wonders after 20 years but I am confident you will get the Ah back up to about 75-80% of their stated rating if the plates are still solid enough.
    If they had good care over the 20 years it might be more, but if they are too far gone you might still need to consider upgrading to new ones one day.


    1 year ago

    Good explanation. However you should have proof read it. You state in several places 'phosphate when you mean sulphate' the whole point of adding the phosphoric is to produce phosphates preferentially, where normally sulphates would form. Hence the term for a buggered battery being 'sulphated up'.


    Reply 1 year ago

    Well, if I mean suphate then I use the term sulfate ;)
    The ting is that once "dead" you already have far too much sulphate on the plates, which reduces the conductivity, increases the internal resistance and lowers performance.
    The phosphates are usually kept in solution but won't form on the plates.
    In return they cause a chemical reaction that reduces the phosphate layer during the charging process.
    It works by a sustitution reaction but I guess explaining this in too much detail would be just plain boring for most people.


    Reply 1 year ago

    Many even lead in sulfuric acid 30 percent forms a weird chemical. from Wiki.
    Do remeber the lead also contains Arsenic in there too so be careful it not just lead salts.


    3 years ago

    Great idea recycling lead oxide layers in batteries for cars. Their should be more warning about soluble lead solutions IE (double layered gloves made from Neprene) may benfit or prevent lead phosphate from being absorbed through the skin.


    Reply 3 years ago

    You are neither getting into contact with the lead, it's byproducts nor the battery acid tself.
    So unless you are planning on dismantling your battery all should be fine.
    Still a pair of nitrlie gloves is always a good idea, same as wearing old clothes as there is always some acid residue on the screw caps ;)


    Reply 1 year ago

    soluble lead solution? what other sort is there?

    Scott Mich
    Scott Mich

    3 years ago

    Do you think the lower the amp the better? And how low!?? I have a charger I can take to mA

    Farmer Bean
    Farmer Bean

    3 years ago

    Is an old style charger ok? I have a 6 amp. Left off the top like you said. I can see it bubbling in there but its not bubbling over. This is a lawnmower battery so I only used 2 ml per cell. Thx Downunder


    Reply 3 years ago

    A bit of bubbling is quite normal during the charge, that's why they have breathing holes.
    Just top up with destilled water once you are finnished charging if a lot of water had turned to gas.