Dead battery, or recoverable?

I bought an 11s3p battery last fall for my Spud build, then didn’t end up trying to use it until recently. I think I may have let it sit too long on the shelf and it died. When I plug it in to the charger it immediately turns green but the battery only puts out 3V’s total. Are 30Q’s that delicate that they can die if left sitting too long?
I tried trickle charging it with 1A for a day but it had no effect on the total voltage. It did not heat up when I charged it. When it is plugged into a charger it outputs a few more volts (~5V total).
I opened the pack and tested each p-group. They each are now contributing .3V’s to the total, as shown here:

Is it possible that the BMS isn’t functioning properly? Or are these the obvious symptoms of neglected cells and there’s nothing to do but recycle them properly?

RIP, your battery.
Any cells that drop below something like 2.5v spells death for 30q’s.

1 Like

Lesson learned. What is the best practice for care of a battery? Recharge every month or so?

1 Like

Being able to unplug it from your BMS is a plus. As for storage I believe around 60% is safe.

Is it possible that my battery drained it’s power from sitting unplugged on a shelf? Does the BMS draw a small amount of power even when the battery isn’t attached to anything?

Everything you need to know about 30Q…

It’s possible, I have read about it on the other forum. There are many others here who know much more than me though.

I have had a battery fail after storing for a winter, I was able to revive it, only had to replace 1 P group. I believe the P group was bad before hand though. My cells dropped to 2.2v. The bad group was something like .02.

It was probably the bms that slowly drained the cells.

Cells by themselves in a pack (not connected to a bms) or individually dont discharge very much voltage at all and can be stored for a year without any issues.


yes, look up the quiescence draw for your BMS. a good quality BMS is something less than 40mA, but if the ESC is powered the idle draw for the ESC can be something like 100-500mA

1 Like

Do you have an antispark switch on this board?

I always check my boards I am not using to make sure they are around storage charge about once a week

The battery wasn’t attached to anything. I charged it up when I received it, but then left it on a shelf. If I’m not going to use a battery right away, it sounds like the ideal thing to do is drain it down a bit (60%?) somehow, and then check on it once in a while to make sure it’s staying at that level.

was teh BMS connected to the battery/cells?

Yeah, it was built in to the inside of the pack. Only thing exiting the pack was an XT60 and charge leads

hooked up as discharge and charge or discharge only?

those numbers are suspicious. have you tried measuring directly across teh cells?

the fact that absolutely every group is 0.3 Volts seems implausible,
I suspect measurement error or something. No offense, but do you think its possible that you are mistaken?

this will cause max capacity to drop but not this sort of crippling…

You know I’m not sure. I’m not sure if you can tell by the photo I included. My guess is it was discharge only (it was sold by BKB last year with their Spud bundle). I’ll try to get my multimeter in on a few groups and see if I get different numbers.
You’re right that the numbers are odd. Not knowing much about batteries, I was hoping that the BMS was dead and there might be a chance that the cells still have life

I don’t think so. The voltage of the 11th p-group as measured directly from the BMS is the same as the total output voltage on the XT60

wheres all that energy going? somethings fishy for sure. I would say theres enough here to warrant an investigation.
I suggest tracing the leads from the plusl and minun of the cell stack (no BMS) and measuring again there. If it were me, I’d remove the BMS altogether.

1 Like

I double-checked all the leads before they entered the BMS and got the same readings. Then I decided plug the battery back in to the charger, and take readings every 3 minutes. I was noticing small changes in the voltage and thought I might learn something. But the craziest thing happened. After taking a reading every 3 minutes for 30 minutes the voltage on the pack jumped up 24 volts all at once! Check out my chart:

X-axis is time, Y-axis is voltage. It’s like the BMS was only allowing a very small amount of energy in to to the cells every 3 minutes (around .06V) perhaps because it could sense that the cells were completely drained? Then at some point the floodgates shot open. How is it possible the pack could jump that much in 6 minutes time (24 volt increase)? These measurements were taken directly from the cells, not from the BMS. I had previously left this pack charging overnight and the pack never increased over 5V. It’s possible something was disconnected/loose and after ripping open the pack that resolved itself…or maybe it just needed LOTS of time (more than 24 hours) on the charger. Good news is I think I’ll buy some 220mm heat shrink and seal this pack up and I think it will work :slight_smile:

1 Like

Idk if I’d leave the BMS in there. Do you have a noselm number for it? Maybe check if there’s some sort of cutoff.

That’s awesome! Good for you