Preliminary testing of large batteries with DMM and bench supply

Thread Starter

Joe Stavitsky

Joined Apr 5, 2020
I have these to guys. I have no idea what SOC and condition are. I have an autozone a couple miles from me, but I was hoping to do some preliminary testing before dragging them there or resorting to the more advanced testers some of you fine folks recommended in an earlier answer.

The APC battery is an RPC4 (labeled on the top with a barcode. It's listed as 12v but I couldn't find amp hours.

My bench supply is rated for 30Vmax and 5Amax. As long as it's safe, I don't really care if I need to leave the batteries hooked up for a week or 2. Anything is better than dragging them 2 miles or worse calling an uber for that nonsense.

Thanks so much




Joined Jun 19, 2012
Set the voltage on your PSU to 14.4V, set the current limit for 1A, let it stew for a few days.

Then see if the battery holds a charge with some car headlamps as a load.


Joined Aug 7, 2020
Measure the terminal voltage as they are. If it is less than 11V don't bother taking them home - they will never recover.


Joined Nov 6, 2012
Is one headlamp enough? If not, how many?
What is the expected Load that the Batteries will be Powering ?
A single Car Headlight is usually ~55-Watts, which means a 5-Amp-Load,
that's not a terribly heavy Load for a large Battery, so,
if they can't maintain at least ~12-Volts powering a Car-Headlight, then they're trashed.

OOOps ........ I just double checked the Pictures,
those are out of a UPS unit that somebody was throwing-out, and You got for free,
this means that they're automatically trash.
Don't even bother trying to Charge them.
You need new Batteries.

An excellent, but extremely expensive replacement Battery
would be an "Optima" "Yellow-Top" "Deep-Cycle" Battery,
around ~$300.oo each but with ~5-times, or more, of the Capacity of your original Batteries.
They're completely Sealed, and will last more than ~5-years.


Joined Aug 7, 2020
17Ah is not a large battery!
I agree with @LowQCab about the UPS.
UPSs use batteries rated for a certain life on float charge, and after the specified life they are replaced.
There may be some life left in them, but they are not deep cycle batteries. They are intended to spend the vast majority of their life on float charge and be discharged only very occasionally.