Did I kill my battery?

[Adamlrivard]

I assembled my first DIY LiFePo4 battery using cells purchased from AliExpress advertised as 280 Ah 3.2v cells and I have 4 of them wired in series for a 12v battery. I also have a 120amp Daly BMS connected.

While assembling everything and about ready to close it all up the P- lead from the BMS touched one of the bus bars and arced for a very short time. Immediately after I checked the voltage of each cell and they were all still at 3.2v so I thought I was all set. See bus bar in the picture for the small mark from arcing.

After assembling fully and charging the battery up I connected it to my RV and started running things to do a capacity test. After consuming 115 Ah it seemed like the BMS auto disconnected for low voltage. There was no voltage coming through the BMS so I opened the battery box up and got a reading of 11.55v across the whole battery. Then I read each cell and I got 2.95-3.0 on three of them and one of them was at 2.6v. That low cell is also connected to the bus bar that got arced.

After plugging back into the converter it charged all cells back to 3.2v in what seemed like too short of a time period.

My question is did I do serious damage to the cell(s) or BMS when I arced it? What should I check to find the root of the problem?

 

[sunshine_eggo]

3.2V is the NOMINAL voltage of the cells.

Cells measuring 3.2V are at a low state of charge.

Discharged cells should rapidly hit 3.2X when a charge current is applied. Most charging will occur in the 3.3-3.4V range - I mean a massive amount of it.... so much that it may seem like they'll never increase if charging at low C rates.

At cut-off, cells measuring 2.65, 2.95-3.0 are not horrifying and likely just indicate imbalance.

Since it wasn't mentioned, I'm assuming you didn't top balance. Top balance your cells in accordance with the guide.

Fully charge and then repeat discharge test.

 

[100 Proof]

Your cells are likely fine. Sounds like you didn't top balance. You'll want to get that done. THEN check your capacity.