I decided to closely watch the charging of our M3 LR, which has had to sit outside of the garage the last week. This morning I set up charging when it was 12F out. On a Tesla wall charger with 48 amps, the car has been charging at about 4% per hour vs the normal 12%. The max charge the car is taking is 30 amps currently and it has been warming the batteries for over an hour and still at 30 amps. Sometimes it might pop up to 32-33.
It charged much faster when I plugged it in right after getting home while the batter was warm from use. So, in this cold, I'd suggest charging as soon as you get home if having to leave the car out and pre-condition (rather than charge) just before you have to drive.
Normally, I keep my SoC lower to reduce degradation due to calendar aging, but with these very cold temps, it is less of an issue having a higher SoC than it normally would.
It charged much faster when I plugged it in right after getting home while the batter was warm from use. So, in this cold, I'd suggest charging as soon as you get home if having to leave the car out and pre-condition (rather than charge) just before you have to drive.
Normally, I keep my SoC lower to reduce degradation due to calendar aging, but with these very cold temps, it is less of an issue having a higher SoC than it normally would.