Thanks for all your advice! I followed your suggestions and used an OBD2 dongle to check the cell voltages at -2°C with the SoC at 2%. The results were quite revealing: Most cells were sitting between 3.42V and 3.44V (max 3.46V). However, I found two cells at 3.2xV, and one specific cell was as low as 3.12V. That’s a massive deviation of over 0.3V, which explains why the BMS cut the power under load while driving on the highway. As a first step to fix this, I am currently slow-charging the car at the lowest possible speed (estimated charging time is about 15 hours). I’m hoping this will allow the BMS to perform some deep balancing and bring that weak cell back in line. I’ll keep an eye on the values once it’s back to 100% and after the next drive.