How did you charge initially? Always 60%?
Sentry always on? It could be good to let the car sleep, with the battery disconnected for some hours.
You might need to help the BMS with a calibration, go low( 5-20%), let it sit at least five hours, then charge to 90% an let it sit a few hours. You could also do 100% but then let is sit only one or two hours, then drive it down a bit. Al this with sentry mode off, doors closed and let the car have siome time for itself.
If the BMS was off, this probably would help.
If the battery was charged very high and the car stood long times with 80-90% at high temps( it do not sound like it did, but for info) the capacity could be lost by degradation which do not come back.
After a BMS calibration( sleep at low and high SOC), you could try to charge to 55% daily. I use 55% as it is below a degradation step and most probably reduvce calendar aging. It also get the BMS to think the battery is bigger after some time of daily 55%.
Going down below20% is not bad gor the battery. As long as you do not get stranded due to low SOC, low numbers is not bad.
My M3P ‘21, with the 82.1kWh 2170L.
One year and a couple of days, 31500km:
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