Lead Acid Battery Maintenance and Rejuvenation:
warning:
batteries contain acid that can burn skin and must be treated very carefully. Especially avoid getting it in yours eyes ( I accidentally once had a tiny drop of acid splash into my eyes while working on a car , it hurt..............alot !!) Not a bad idea to have some cooking bicarbonate and normal water handy, the bicarbonate will neutralise the acid quickly in case of accident and water will dilute it or wash it off.

You need to make sure your batteries are in fact absorbed glass matt not gel type batteries before doing any of the things below. I've found that most specialist battery sellers will have no idea if their batteries are agm or gel type. The batteries also do not say on the outside of the case if they are agm or gel type. You need to check the model number with the manufacturer to be 100% sure of the type of battery you have. Jump starter batteries appear to be all absorbed glass matt type.

Over time I'm starting to better understand sealed lead acid absorbed glass matt type batteries. It seems that it is possible to lengthen their life and rejuvenate them though I'm just beginning to mess around with them probably too early to say as yet if its effective over the long term.

Structure of Sealed Lead Acid Absorbed Glass Matt Batteries (sla agm) or (sla )

Another name for these bateries is VRLA ( vent release lead acid )

(note: sealed lead acid gell type cells are not suitable for ebikes they have a very large voltage drop which is slow to come back up again, they can be used but results are nowhere as good as sla agm type).

Sla agm batteries are basically the same as your normal car batteries ( wet cells ). The differences appear to be fairly minor, so you can to some degree use the same techniques as used with car batteries. There may be some chemical differences in the lead/lead oxide but I really have no idea about that side of things.

Some differences and similarities to car batteries:

Although the batteries are called Sealed Lead Acid, they are in fact not completely sealed. And its necessary that the cells are not 100% sealed from the outside air as they work in exactly the same manner as wet cell car batteries ( hydrogen is produced when charging and needs to be released to the atmoshpere ).
So although they look like they are completely sealed you can in fact take off the tops and see the 6 vent holes for each battery section. The vent holes have small rubber tops on them which allow hydrogen to escape when charging. So the first thing to note is that sla agm batteries will over time loose electrolyte ( water in this case ) to the atmosphere, through two means: 1. bubbling off of hydrogen and evaporation of water vapour.

Postcript: on further reading about sla agm batteries, it appears that the oxygen and hydrogen produced in the battery play an important role in the proper functioning of the battery. The rubber plugs on the vents of each cells maintain a low pressure inside the cells which aids the reactions involving hyrdrogen and oxygen. If the pressure builds up too much then the rubber plugs simply expand due to pressure and the gas pressure is realeased.

So one method of maintenance is to replemish the lost electrolyte. Quite often chargers of incorrect ratings will be used (too high an amp rating )and electrolyte can be lost quite quickly ( over a few months ). Also the slower you charge these batteries the less electrolyte is lost via water vapour being given off. If a battery is quite warm after charging it will be loosing water vapour to the atmosphere. Its also important not to flood the matting with too much electrolyte as its the microscopic size pores in the matting that allows the gases to move and interact. So flooding the matting with electrolyte will give rise to excess production of gases during charging, so it looks like a bit of an art to rejuvenating these batteries.

 The matting used inbetween the plates in sla agm batteries tends to be asbestos fibre. So great care should be taken if rejuvenating sla batteries. Sometimes the asbestos is used around the plug holes to soak up any electrolyte that might come out of the plug holes. Inhaled asbestos fibre can lead to asbestosis of the lungs and so it should be treated with care.I believe higher quality sla agm batteries may use fibreglass matting but I'm not 100% sure.

The function of the asbestos matting is to absorb the electrolyte so that it cannot move around like in a car battery. It acts like a sponge which holds onto the electrolyte without effecting its electrical properties. So you can turn one of these batteries upside down and the asbestos will hold on to the electrolyte, hence it doesn't run out of the battery. But the matting also has other functions, as mentioned above one is allowing transfer of gases through the minute holes (pores) in the matting.

Its possible that the hydrogen under low pressure in the cells when charging will recombine to form water and somewhat replemish the electrolyte but loss of electrolyte does appear to be an issue with the lifespan of these batteries.

Postscript: seems recombination of hydrogen and oxygen and other reactions of these gases with the lead plates is facilitated by the matting.

Rejuvenating Sealed Lead Acid Absorbed Glass Matt Batteries

You can get quite good results rejuvenating these batteries as long as their voltage is not too low to begin with. If they have a voltage of 12.4 to 12.5volts after charging you can rejuvenate them to a reasonable degree. Any lower than that and its not likely you will get decent results. If there is some physical damage inside the battery ( such as some plates are shorting out then these measures will likely do nothing to improve them)

Theres a few things you can do:

1. replemish the electrolyte: adding demineralised water or better fresh battery electrolyte ( from car parts shops ) (sulphuric acid ) being careful not to overfill and flood the matting

2. give the batteries two deep discharge cylces down to 10.5volts, but no lower or battery may be permanently damaged ( removes some of the sulphate deposits)

3. use a desulphator to clean the sulphate deposits off the plates

Using any or all of the above methods with assist with battery life or rejuvenation, I'll outline below how to go about doing these things. Please note that it can take some time to do all of the above things. It can also be done quite quickly depending on which method you use.

Firstly you will need to open up the batteries lids. Usually the lids have some glue underneath them to hold them in place. So its quite possible the lid will break when you try to get it off, I've found 12ahr size batteries the lids can come off quite easily without damage, but larger size batteries are more difficult to get the lids off without breaking them.

Find a very thin small screwdriver, place it in the small crack around the lid and lever up the lid.

Below 12v 12ahr ebike battery: lid was removed with breaking it

Larger format 12v 40ahr sla agm battery lid was damaged during its removal.

 Note: If there is asbestos matting ( fibre ) around the plug holes store it in air tight container and remove it carefully so as to not let any fibres become
airborne.

Just a note on the matting material. I suspect the fibre placed around the plug holes is the same fibre used in the batteries. It has some unusual properties when mixed with electrolyte. It can take the fibre a very long time  to absorb the electrolyte. Below is a picutre of asbestos fibre (which is dry in the picture above) that has been sitting in electrolyte for over one month and it can be seen that parts of the asbestos have still not absorbed the electrolyte. The areas which have not absorbed electrolyte appear bright white, the areas that have absorbed electrolyte appear clearish or like jelly.

So its very likely that an sla agm which has lost capacity will have some areas of dry asbestos matting between the plates. Replemeshing the electrolyte it may take a long time for the asbestos to completely absorb the electrolyte though I think a few days is enough time for the dry asbestos to become partially filled up again with electroylte. Even overnight is enough time for some of the asbestos to absorb new electrolyte. But there may be areas that will remain dry for a very long time, this will influence the batteries capacity so over time it can be expected as more electrolyte is absorbed that further increases in capacity will occur.
I have in fact found this to be the case with the large 40ahr batteries pictured above, which after sitting for approximately a month the capacity with charge and discharge cycles (periodically over that time ) has continued to increase.

How to Refill the Sla agm batteries with electrolyte: (will add some pics to this section later on)

Postcript:  On reading some technical material on sla agm batteries I've learnt that overfilling the batteries will cause the matting to become flooded with electrolyte, the microscopic pores in the matting are very important in the correct functioning of the batteries, so its best to fill to the top of the plates or just over then tip out the excess acid. Also too high a concentration of acid can effect the batteries adversely, so its probably best to add just a small amount of new acid to the cells then top up mainly with demineralised water, not just use new electrolyte to refill the batteries.

1. buy some demineralised water and some new electrolyte ( in australia super cheap auto parts and similar shops sell it ). Better results will probably be gained by puting new electrolyte rather than just demineralised water. If you dont like dealing with acid ( electrolyte ) just use the demineralised water.

2. Buy a large syringe from a chemist ( with no needle on it ) ( it might be useful to also buy one that has a needle on it but not necessary )

3. Find a glass container ( it will not react with the electrolyte ), place some electroylte in the glass jar and use the syringe to put it into each vent of the battery.
Continue filling each vent until the electrolyte reaches the top of the vents. Now just let the batteries stand like that overnight. You will most likely notice that some of the vents the electolyte level has dropped over night. Refill these to the top again and let sit for another night. Its interesting that the vent closest to the positive end of the battery will have lost the most electrolyte during the life of the battery thus far. Its likely to be the warmest cell during charging and it also has a higher amount of electrons flowing through it during discharge and during charge so not too surprisingly really.

4. Once your satisfied the dry parts of the asbestos have absorbed some new electrolyte ( its very likely there will still be some dry patches of matting in the battery at this stage ) it will now be necessary to remove the excess electrolyte. Its important that you take out the excess electrolyte that is sitting above the matting.  There are two ways to remove the excess:
        a. with a syringe with a needle on it ( very tedious and hard to judge when you have reached the top of the matting )
        b. by tipping out the excess acid by turning the battery upside down. I find puting on areas of the garden that have weeds is a good place for the acid. One thing though due to how the vent holes are made, turning the battery upside down will not remove all the excess electrolyte. I found it necessary to drill small 5mm diameter holes in the top of the cases (near the vent holes ) to remove all the excess acid. 

5. Because the pressure in the battery plays a role in gase exchange and reactions, the drilled holes must be sealed up again. To maintain pressure in the battery ( its only a fairly low pressure ). I just use a soldering iron which melts the plastic near the holes i've drilled, well makes it soft enough to push it back into/over the holes, thus sealing the battery again. You can test if the battery is sealed by put it on a charger, as the gas pressure builds up you will see some acid coming out of any holes that still remain, the rubber stoppers can also 'pop' off during charging if the lid is not put back on the battery.

Also I've noticed that occassionally when recharging a battery after puting new electrolyte that you can get a cell that will push acid out , its probably gases trying to escape and pushing some acid above the it, so initially , the first charge after puting new water or electrolyte in a battery, its a good idea to keep an eye on the battery , if any cells start to push acid out of the vents ( it happens fairly slowly and I just soak up with toilet paper until the excess acid stops coming out of a cell.
But this only occured before i had tipped out the excess acid, if the excess has been tipped out then it shouldn't be a problem.

How to Rejuvenate a Sad Sla Agm Battery:

There are two methods:
1. do two deep cycle discharges and slow recharges
2. use a commercial desulphator unit ( I have desulphator units I can supply see link)
Best results if you use both methods above.

Method 1: Two Deep Cycles
1. you will need some way to discharge you battery down to 10.5volts. Its very important that you measure what voltage you discharge the battery down to, so you will need a voltmeter set up on the batteries while you are discharging it. Do not go below 10.5volts........battery may be completely stuffed if you do.
You can either discharge each battery separately or do a few in series at one time. Probably best to do separately but takes alot longer to do that way.
I just use light globes of suitable ratings to discharge the batteries down to 10.5volts. For 12ahr size batteries I used car headlight globes which were 12v and they used about 5amps of current ( approx 50watts being drawn out of the batteries ). For larger batteries you could use a number of headlights in parallel to quicken the process.

2. Once the battery reaches 10.5volts immediately recharge it, preferably with a low amperage charger ( 1amp or so ) but I dont think is that important how quickly its recharged. Once it reaches its maximum voltage ( which should be higher than before you did the deep cycle ), repeat the process. Discharge it again down to 10.5volts. You will notice (if the battery wasn't too far gone ) that the second recharge will take alot longer as its gained capacity by some sulphate deposits being knocked off the batteries and allowing the lead to interact with the acid again.

Method 2:
Use a commercial desulphator. The units I have on website you simply connect to the fully charged battery. The led on the desulphator will start off green and then turn to red when the battery has reached a certain voltage ( not a very low voltage like a deep cycle , it only takes a short time for the red light to come on). Recharge the battery when the led turns red then use the desulphator again, repeat this process about 6 times.

Note: when puting the lids back on the batteries, if a glue is used do not seal off the whole area of the lids, they must have access to the outside air, so just a few dabs of glue here and there ( glue that can be in contact with battery acid preferable, if any happens to get out of the vents ).

At this stage I have not done alot of testing on how the batteries capacities have increased in ebike usage. I have only measured how long the light globes have taken to discharge during deep cycles as a measure of the capacity. But the results are looking very promising. Over the next few months I will be able to use the rejuvenated batteries in ebikes and see how they perform.

Test Data:

I have recorded some data on the 12ahr battery deep cycle tests which is outlined below:

Testing on 4 lots of 12v 12ahr batteries. These batteries were discarded batteries from a local ebike shop  and have been sitting in my garage for a couple of years now. I've never used them on an ebike they were used by the initial owners though and discarded after an unknown amount of usage/time. I have no idea of the date of their initial manufacture but was possibly in 2005 would be my guesstimate.

 

Was quite happy with these first test results in which I only used a commercial desulphator unit and distilled water ( from a chemist shop) to refill the acid. At that stage I didn't realise demineralised water is better and readily available and cheap. A new sla agm battery should have a fully charged voltage (after taking off charger and leaving sit for a while it will drop to a stable voltage) of over 13volts approx 13.1-13.3volts . So am quite happy the voltages have come back up quite alot. Battery 1 and Battery 2 had come back up to 13v pretty much. Also you can see the very high increase in voltages after adding water and recharging, so I suspect that lack of electrolyte plays a large role in the loss of capacity of sla agm batteries.

First I have to say thanks to Craig at Eazyride Bikes in Newcastle for telling me about his deep cycling methods to rejuvenate sla agm batteries, he uses a commercial discharger that uses light globes to discharge 4 sla agm in series and automatically cuts off when batteries reach about 10.5volts each, it also measures the total ahrs delivered and displays the result on a readout screen.

Next I did one deepish cycle of the above batteries to see if the capacity could be increased. At this stage I had no idea what their capacities were ( in ahrs ). The batteries in their original condition should have been 14ahr. My first attempt at deep cycling used all 4 batteries in series in a 48v setup (based on Craigs method) I connected the batteries two two small 48v globes and measured the battery voltage over time. When discharging the amps being drawn by the two small lights was 0.12amp ( 120mA). A very small current but i had to start somewhere was all I had handy at the time. Obviously it took a long time for the batteries to discharge at this rate (about 3 days ).

Results: Using approx. 6watt discharge power from two small 48v lightglobes (voltages shown below)

From the data it can be seen battery 2 has consistently lower voltage so maybe some problem with that battery the others batteries seem all very similar.
Total ahrs of the batteries is Amps times Time(hrs) ,
Capacity = 0.12 * 66.5 = 7.98 or approximately 8 ahrs of capacity after using the commercial desulphator.

Next I did I deep cycle of each battery separately using a car headlight globe to discharge. Average discharge rate ( very roughly was about 4.5amps by the car headlight globe giving approx a 50-60watt discharge source). A rough calculation gave about 11 to 12ahr capacity ( so that would be due to the 0.12amp deep cycle previously) Battery1 I accidentally discharged down to about 6v ( the voltage drops of very rapidly at the end of the discharge but the other batteries I kept closer eye on them and stopped discharging at 10.5v or very close to it.

Then I recharged each battery very slowly with a 500mA jump starter charger which took a very long time (over 24hrs )!! (Battery1 came back up to 13.1volts after letting stabilise after charge, unfortunately I didn't write down what the other batteries came back up to but they were all higher than previously). Indicating the battery capacity had indeed risen considerably. Next I will have to use the batteries in an ebike with a drain brain meter and get the useable amphours that the batteries have after a deep cycle with the car headlight.

Below is a rough graph of the discharge curve for battery 1 ( which I took down to about 6volts ) I also wrote down the data for the other batteries but I dont see alot of point in puting all the data up. Looks pretty similar to battery1 except I stopped discharging at 10.5volt.

So that was my first attempt. Now I'm trying with  electrolyte to top up the cells, and discharge with car headlight globes. But the results look promising indeed. A test in an ebike will tell if the batteries are permanently rejuvenated or whether it is only a temporary fix for a short period. The reason I say that is because Ray of NSW tried with some sla agm batteries which were good for a short time, then rapidly deteriorated back to a poor capacity. I'm just keeping the batteries topped up until I can get time to install on a bike and start using them.
 

Below: deep cycling sla agm batteries with car headlight. Volts and amps were recorded (volts shown on multimeter in picture)

Just a note the experiments with rejuvenating the larger format 40ahr golf buggy batteries also looks very promising. They are now accepting high rates of charge for long periods. Basically the same methods as above were used but acid was added instead of water. I'm also doing some 17ahr batteries

31April07: Used one set of batteries that had been rejuvenated just with distilled water ( not demineralised ), on recharging the batteries, the charger took a very long time to recharge ( overnight using a 3amp charger ) on 4 lots of 12ahr batteries. The charger is a bit too much current for starters, but strangely the batteries seemed to not get to full charge, the charger stayed at about 80% full. On doing some reading it seems possible that I've flooded the glass matt, and batteries wont charge up to full voltage, they will be venting off hydrogen and oxygen. Also the batteries were getting warm, which I think may also indicate flooding of the glass matt ( the air pores in the matting are filled with electrolyte, the air pores play a major role in the exchange of gases and correct functioning of the cells ). Over time the excess water will be gassed off and the pores will start to appear again, so I imagine after a number of uses of the batteries in a bike, then recharges they will start to come up to correct voltages. So will post some reports over time on what occurs.

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