I Think I Screwed Up My Battery - Please Help

Here is what happened:

I rode my bike for a while yesterday and only used half of the charge. Usually I just disconnect it and put it in the charger to top it off.

Yesterday I was distracted and just left it. Today I spent some time truing the wheel and then gave it some throttle and got nothing. so I put it into the charger and instantly the red light came on. I broke out the volt meter and it is registering zero on the volt meter.

The battery is 2 Bosch fatpack 36v 2.0 amp hours in parallel for 4 amp hours. The batteries are Samsung 3.7v 1ah 18650s. Are these now toast? The throttle was not on but the batteries were connected to the controller. That is all I know.

If there is some way to put a charge back in them please help. I have another 4 ah setup that is fine. Is there any way to use it to get a charge in them or should I just chuck them and chalk it up as a lesson learned?

Are the actual cells reading zero? If so, I'd call that toast. Even if you can recharge them, I wouldn't trust them for anything "high output"--their resistance and such has probably changed significantly.

If they have a BMS in there that has simply shut off at it's LVC, then the cells themselves may be fine, but you'd have to check their individual voltages to see.

It's possible that if the drain was low enough, they might be reviable and usable.


FWIW, someone turned on my lights at work one day more than a year ago I think it was now, and killed my EIG NMC 20Ah 12V lighting pack to zero volts per cell. Just to see what happened, I recharged them with a constant current constant voltage lab PSU (outside, on brick, under a metal bucket, only when i was able to be there to watch them, away from the house) slowly over several days, at very low current (100-250mA, I think--it should be in my CrazyBike2 thread somewhere). Eventually they charged up to their nominal "empty" voltage, and I increased the current to them, and eventaully put a full 20Ah back in. THen I did a discharge test using a Venom RC charger from SoSauty, and a more normal recharge, and they seemed almost normal, except for what is certainly higher internal resistance, and more sag under even moderate (less than 1C) loads.

I kept using htem as the lighting pack, expecting the worst every day, but nothing bad has happened to them yet, even charging them at the fastest rate the Accucell6 from EbikeFanatic could support, about 5A peak. I've never tried charging them faster than that, or discharging them with motors or other really high loads, just the lighting and occasionally air compressor.

Even today, they still work as well as they did then, and were used as my lighting pack up until a couple of months or so ago, when I moved to a DC-DC converter for most of the stuff--but I still carry the pack to run my air compressor in case I get a flat, and as a backup in case the DC-DC fails.


I don't know the bosch cells, but there's a fair bit of data on them here on ES if you poke around, so someone has probably done this test before.

My bikes use less than 3w just sitting with controller on. So 24 hrs would be only 72 wh.

But if you only had 40 wh left, whoops. Half your pack would be only 70 wh or so. So likely it was low enough to not last 24 hours.

I'm confused about one thing though, wouldn't your fatpacks have an internal bms that would prevent overdischarge? Maybe the cells aren't really at zero, but just shut off. So if that's the case, why won't they charge? Does the red light on your charger mean it won't charge? Are they charging, but the bms won't turn on yet?

If they are actually zero, they are toast. Know from personal experience. It is possible you can force a charge, but the capacity will be GREATLY diminished and the chance of a battery failure, possibly resulting in a battery fire, is very real. Chuck them out.

well they sat for a while (off the charger) and now they are reading 22.4v. I put them back in the charger and it looks like they may be charging. I feel a little foolish but I know my volt meter registered less than 1 volt earlier. Strange.

Thank you for all of the input, it was helpful.

the BMS would disconnect the outputs when one cell dropped below the LVC. so your voltmeter was not in contact with the battery when you measured 1V.

when you started charging the low cell climbed above the LVC and the BMS turned on again so you can now measure the battery voltage.

I had a situation like that with my 6 parallel fatpacks with Sony VT cells. Left the controller on for a week and drained all packs to zero. Charged them with a NiCad charger to start them and then when they were around 20 volts they took a charge from the Bosch charger to around 40.5 volts. This was 2 years ago and, while they are not perfect, ( within 5 mohms) they work fine today. These are not the same cells as you have, but it is usually worth a try to restore non- hobby lipo batts. HK Lipo, no thanks.
otherDoc

The batteries charged up fine. No heat.

I took the bike for a ride to see if I lost any capacity and I am still getting around 2 miles per amp hour. I ran them until the controller turned off and then recharged them again.

They appear to be fine. I think it may actually be my charger. I have other fat pack clones that the charger would not charge but now it will charge them.

There is some funny business going on with my set-up. I think I have to look into it.

Safe to say that it's very likely you just read 0v because the pack bms tripped. It may be that the charger does something different than usual when you charge a pack with the bms tripped.