Electronics > Power/Renewable Energy/EV's

10 year old rechargeable acid battery

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I just took out this old battery from the casing of originally what used to be a car engine jump starter.
It used to be recharged for 13.8V, and used to output the DC to power the other electric gadgets giving out 12V, 9V and 3V.
It is about 10 years old.  Now it was not charging well at all.  It would try to be recharged, and then the fully  charged light would come on.
When it then connected to any device, it would return to LOW power mode immediately.

Today I disassembled the casing, and there was this acid battery rated at 13.V.  When measured the output voltage of the battery with DMM, it reads 9V.
Could this battery be used for 9V?    Is there a way to revive this battery? Or should it be discarded?

I am going to order a new acid battery of 12V 9AH from Amazon, and connect it to the old jump starter, because it has all these buttons for charging, and outputs for 3, 6, 9, 12V (cigarette socket output).

Rick Law:
I am no expert, but I have experimented with battery revival half a dozen times.  This is not an expert-opinion but merely sharing my non-expert insights from those fruitless efforts.

Car jumper battery is probably SLA (seal lead acid) or GEL.  12 volt is actually 6 battery lead acid cells in series each of 2 volt.  So 12V car battery is a battery pack consist of 6 cells.  My understanding is GEL and SLA are similar in the way they work except for how the acid is "held" inside the cell, as a gel or as a liquid.

When it is below 10V, you are more than 2V from 12V.  When you have only 9V, likely, the weakest cell is stone-dead, and at least one more cell is below 2V.  The dead cell(s) will work against you when you try to use the remaining "working" ones. (see notes at bottom if you want to know how it work against you.)

In my tests in trying to revive 1/2 dozen of old SLA's (three are from car-jumper packs), the other three from UPS - all are SLAs (not gel) based on visible fluid presence.  All but one were dead for > 1year.  Some holding voltage at 5v ish, some holding below 2v.  The best dead one was last known to be alive and charged about a 1 year ago (before date of attempted revival).  That one was holding voltage at 10-10.5v. 

- For some, slow (drip) charge often bring it back to 12V.  it could hold some charge, but single digit percent of rated.  Best case I got from the not-too-dead one (rated at 22AH) was below 1AH.

- for some, it may rise to 12V in mere seconds.  It is because the charge it can hold is low so it is "full" quick.  Like a gas thank full of rocks, you can fill the tank quick but holds little gasoline.  With just a small charge, it drops back to way below 12V really quick -- in sub-second or within seconds when discharge started, it is done discharging (my worst was under 1V, so all cells were dead - upon disconnect of charge cable, self-discharge will bring it back down to 1V within minutes).

- Renewing the battery acid (you can buy that at auto stores) doesn't help... reason below later

- Acid in the battery is sulfuric acid, around 50% pure sulfuric acid if memory serves.  Discharged battery start reacting and deposit the sulfur on the lead plate.  De-sulfation with those "pulse desulfator" modules does work but just very very little - it gives a flash of life (a few percent more) for a cycle or two than back to darkness.  Further de-sulfation will do less and less... same reason, below

- It appears to me that the lead-plate is too well coated with sulfation.  Pulse is not going to "break it up".  One could consider sanding it off (as some battery re-manufacturers may do), but that is an extensive job and a rather dirty one.  Then there is also the consideration: is there enough lead still left on that lead-plate to be useful.

So, all in all, it is not worth the effort.  My best was "revive" a 22AH rated battery to give me less than 1AH  (At below 10.5V, I terminate and sum up the numbers), but it would be easier and more predictable to use a few AA or 18650 batteries for that.

Notes: How the dead cell work against you
If you want to understand how it works against you: Draw a diagram of 6 cells and a load (so 7 boxes) with a line joining the boxes and the load in a circular chain, write down the + and - on each box that represents a cell.  Now follow the current in the circle, you will see that on a dead cell (regardless of which one of the 6 you pick as bad), the current flow for that box will be reverse charging it.  It can't do much "push against you" since it has little charge, but it certainly will "resist" your effort.

The old post here I wrote on that desulfation test:

Edit: Reviewed my old thread and correct a few numbers I type here. (Number typed here came from memory whereas the old tread was from actual notes at the time, so the old one is accurate).  Yes there were 6 total.  My old thread said 3 because the other 3 is so "stone-dead" I did not seriously tried to revive them.  It did get the desulfation but no serious notes was taken after seeing how little charge it held.

Great explanation on the topic - thanks !!

I started charging the 10 year old lead acid battery taken out of the car jump starter casing with my lab power supply rated at 10A, 1V - 30V.
When the PSU was set to 13V, and connected to the old battery, there was nothing on the amp display on the PSU, meaning it was not charging at all.
I slowly increased the voltage to 15V, 17V, and still nothing, but when it is 20V, there was amp reading  350mA.   So it was charging at 20V, and drawing 350mA.
I then decreased the voltage to 14.8V, and the amp went down to 150mA.   I thought that would be about good amp reading for the slow recharging.
And it is charging at that right now - I will leave it for about 24 hours and until the amp reading decreases to 0mA.

It seems the old 10 year old lead acid battery needed some kick off with the higher input voltage around 20V, and it started recharging, and showed the sign of life.   I have already recharged another old Lead Acid battery this way, and it seems now working OK, so I am following the exact same method.   Will update how they will run - they may only work briefly and fail or die again. I am not sure at the moment.  But if they keep working good again, then it will save me buying new batteries at about £20 - £25 each.


If you pry off the sealed plastic cap there will be one way rubber plugs on each cell. Common failure is the gell dries out. I have recovered a small number of these by removing the caps and adding distilled water.  Allow at least two days before attempting any charging.  There is no recovery from severely sulphated plates.


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