Had a strange thing happen to me a few days ago.
Left my house with a full charge to go to the mall 5km away. Normally I charge to 80% but some plans changed at the last minute.
It's cold and I was running the heater so I arrived with about 82%.
When I came back to the car about half an hour later when I started the car the SoC indicator started out blank and I slowly saw the bars appear. I've seen this behavior with a dead 12V battery but mine is only a few months old. When I finished I had one bar less than before(13, I had 24 when I parked). I checked OVMS and it now showed 72% SoC. I checked the BMS and cell #76 was way lower than the others. The others were much closer. I drove home and lost about 20km on the RR on a 5km drive.
I charged it back up to 80% and it seems fine now. I did a risky 100+km trip in the cold today and made it back with 2 DC charge sessions. I watched the BMS constantly but the cells were relatively level, and #76 was no different than the others.
I'm doing a full charge from 20% now to run the cell balancing, it's been about a week since I ran it last.
Is one of my battery cells dying or is it just a fluke. My 2012 has about 48,000 kms now.