I have a 55kWh Tesla Model 3 pack from a 2020 car, and I've had it on a bench for the past two years or so...slow project progress! Being newish to HV batteries and keeping my distance, I didn't run them down to any storage voltage, all cells about 3.96V. All four modules are disconnected from each other and raised off the bench, and taped up.
I periodically measure the voltage of the modules and they've always stayed steady and similar across modules. Back a couple of months ago, I had some tap wires soldered to the BMB slave board pads for use with an Orion 2 BMS. Checked all cell voltages before and after and all remained even with no sign of issues. I never connected these tap wires to anything since, while I continued working on other parts of the project.
Recently I was doing some testing of all 96 cell voltages and now find that one cell on module 4 has dropped to approx 0.4V! Not good. No visual signs of any issues around the module or on the BMB slave board. I've read other threads about TM3 battery cells damaged where people were considering splitting the module for smaller voltage packs etc.
So I expect this is unrepeatable as I wouldn't be on for isolating the cell (trying the split it from the neighboring cells) to try resuscitate it on its own and bring it back to the voltage of the other cells, and so I'll have to see about finding a spare module somewhere.
- My query is, does this make sense? Is this something that can randomly happen on quality packs or would there have to be some external issue that caused this?
- Might there be a way to safely try resuscitate that cell?