“What happens if you are traveling up the grapevine and traffic is halted for hours because of a snow storm?”
Steady-state heating is about one kw. Tesla says less. Assuming a 75 kwhr battery:
75 kwhr / ke = 75 hrs.
Just using the heated seats draws much less.
I've read if you crank up the heater it is anywhere from 4 to 6.5 kwh.