An EV can lose 12% of its range in cold weather, but if the heater has to be on full to keep warm, that loss can jump to 41%.One negative I heard is that if it's too cold out the battery drains faster than a charger can charge it, is that true?
A low drag electric heater is essential in an EV, and one manufacturer suggests you use the seat warmer to supplement the main heater and cut down battery loss.
Full charge times increase significantly in cold weather with an outside lower battery temperature also.