Wonky voltage readings?!?


Feb 4, 2021
I have a small LiFePO4 battery (12.8v, 12Ah) that is designed to replace a small lead-acid battery in something like a gate opener, wildlife feeder, etc. I charged the battery initially to 14.4v, and it settled to about 14.35v where it sat at steady voltage for a few weeks without any signs of self-discharge. Then I deployed it -- where it basically did not work at all.

I pulled the battery last night thinking it was simply discharged or internally shorted out. I put my multimeter on it and got a reading over 84v. This makes NO SENSE to me -- how in the world can a 4s / 12.8v nominal battery possibly register 84v?!? I verified my multimeter on several other batteries, and it read them all precisely. Worried that the battery might somehow be dangerous, I placed it outside on the driveway overnight -- if it burst into flames, it wouldn't hurt anything there. It was pretty chilly overnight -- 35F. This morning I tested the battery again and it was registering about 22v cold. I left it outside for the day. Then this evening I brought it the battery in and let it warm up to room temperature of about 68F. I just tested it and it's now registering even higher at 96v.

Has anyone ever seen anything like this? Other than the obvious -- the battery is junk -- what is going on or causing this??? I've never seen anything like it.

Thanks --
Cheers, John
I have a small LiFePO4 battery .... Worried that the battery might somehow be dangerous, I placed it outside on the driveway overnight -- if it burst into flames,
LiFePO4's don't burst into flames. They just generally just "smoke" a bit as they off-gas.

As for the weird voltage???? That is odd. It would almost seem like they have the cells wired up wrong internally, but I think those a 4s1p, so that's not really possible.

Can you post pictures of the battery and make/model and where you got it from?
What i've seen, is that the MOSFETs leak a tiny bit of current when it shuts the output off. Resulting in a voltage being measurable. Try to attach a tiny load like a 12v car light bulb or something similar and read the voltage again.
Thanks, gents. I knew that LiFePO4 chemistry was supposed to be safer, but I'm just paranoid generally. Most of my experience is with Li-Ion batteries.

Here's a link to the model of battery in question: https://www.amazon.com/gp/product/B0C4P1NPXZ/

I have e-mailed the manufacturer at no less than three e-mail addresses, and so far have not had a response. I'll update if I get one. I'll also measure the voltage again tonight when I get home and see what it's reading. Oberfail, good suggestion on load -- I'll find a 12v something or other laying around and try to run your experiment as well. And if nothing else, I'll tear the battery down and see what the individual cells read. I have to think it was wired properly at some point, or I wouldn't have been able to charge it to 14.4v and have it hold charge for a couple of weeks. Very odd. Thanks again for the input!

Cheers, John


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Check/replace the multimeter's own batteries, you can get flakey results if they are low.
Otherwise, if the BMS or something else inside has gone open cct, the voltage might float high like this.
84V is a pretty good effort though!
Correct me if i am wrong.
I think the display is stating 84.5 m V.

It would make some more sense, that your battery is more or less useless.
A blown fuse in your battery?
Your battery did not take a charge?
Your battery refuses to give any power?

But 84.5 whole volts.....dang...out a 12v battery?!?!?
I dont think it is to blame your dmm battery.
When that one is low you will get some odd measurements like 5 tp 10% off, but to 84?!?!?

i just hope you just forget to put the charger on.
14.4v, and it settled to about 14.35v

LiFePO4 battery (12.8v, 12Ah) t
That is nominal V, max V would be: 4*3.65V= 14.6V
Minimum = 4*2.8v = 11.2V

Advised SOH is between 9.5% and 90% aka 12.0v to 13.4V for a 8000 cycle life
Beyond 13.8v (99%) is not advised for long cycle life, it shorts it down to 4-5000 cycles they say.
Correct me if i am wrong.
I think the display is stating 84.5 m V.

I'll be danged -- you read better than I do, and everyone else that missed the teeny-tiny "m" on the multimeter screen!

So reading .084V (more or less 0v) makes more sense than reading 84v for sure -- I couldn't figure out how that was physically possible, and I'm pretty sure it's not unless there's some kind of electronic voodoo going on inside the battery (such as with the BMS). Which leads me to my next guess -- that the failure must have something to do with the internal BMS in the battery. I haven't actually had time to fiddle with it since I originally posted. There's no (logical) way that the battery actually went to 0v. It was deployed only very briefly, in a very low-draw / low-demand application, and it was fully or nearly-fully charged when it was installed.

Yep, my new theory is that the BMS freaked out for some reason and basically turned the battery off. Why, or whether it can be redeemed...that's the next chapter. I'll update when I get a chance to look at it.

Thanks again for pointing out what I missed -- it seems so obvious once you see it!!

Cheers, John