Hello. I have several 12V batteries taken from UPS units. I know that one of them is probably good since it was taken before it started failing, and the rest are so-so. But, all of them have been sitting on a shelf for a couple of years at least. Measured them with the multimeter, they're all around 4V presently, and since I'm thinking of using them for arduino projects, what I need is more or less that. Two are generic nonames, and one is an APC battery.
Thing is, I tried charging them by putting them on a 12V supply with a diode in there to prevent reverse current. Output from the supply is 13.8VDC measured at the battery terminals. Hooked up the multimeter in amps mode: one of the nonames is taking 130 mA, and the other two are at zero. No current is flowing despite the battery being at 4V and the supply at 13.8.
My question, are those two that show no current simply so dead that they can't take a charge, or is there some kind of magic you have to work to tell the battery you're about to charge it? Especially curious about the APC one, which I figure might have some kind of IC hidden in there?
Measured the one that was taking current, that one's up to 10V presently. The others, didn't venture to try leaving them plugged in for a while, given that they don't want to move a single mA.
One trick to revive batteries is to hook them to a charger in parallel to a working car battery.
Another one is to top them up with fresh electrolyte (if you can acquire some).
I agree, they usually go "dry", there is a vent for any gases to vent out when they begin to die.
Recharging just turns electrical energy, if there is any charge current, into heat.
My work has a contract with a local government organisation, to annually service and check their many (20+) UPS, after 4 years service we swap batteries out.
Previously they would wait until the UPS failed, caused major revenue loss due to lack of service, then get the batteries replaced, 50% of the time the UPS had died also.
A large number of (cheaper) modern chargers has a minimum required (dead) battery voltage to actually start the charge process when connected (mine is also like that).
By hooking a "working" battery in parallel you enable the charger and can then disconnect the parallel, working, battery.
The process will certainly not resurrect a truly dead battery, but will allow changing a "flat" one.
This too, but from the videos i have seen, i got the impression that the working battery is used as a high current source to slowly chip at whatever harmful deposits accumulated on the electrodes.
Others connect welders and such for a few seconds, for battery revival and maintenance.
One thing i know for sure is, that simply topping up with distilled or deionised water don't help.
Unfortunately, i could not find anyone selling electrolyte in my area, and i don't feel confident enough to mix it myself.
Distilled "battery" water would have been my first thought too. I can get that one at the gas station, but from what I'm seeing that's not the same as electrolyte.
These batteries have a lid and caps exposing the insides. I suppose if there was leftover electrolyte residue in there, the water might work?
Asking out of simple curiosity, since I'm probably gonna go the "spend $20 on a new one route" this time.
A lead/acid battery makes the 'electrolyte' ( H₂SO₄) while it charges.
Problem with old SLA batteries is warping/shedding/sulfation of the electrodes.
That can't be reversed.
You can get a lead/acid battery to life again,
but you're stuck with low capacity and high self-discharge.
And yes, I tried topping up with a seringe, and all the other tricks.
Waste of time.
Leo..
