No different than gas vehicles running out of fuel.

Do the math and let's say theres even 50 percent charge of a 60kwh pack...and you just blast a 1000w of heat constantly....thats still 30 hours of heating at 1kw of power lol.

Gas vehicles burn .25 to .5 gallons per hour so uh...that 16 gallon tank completely topped off is 'only' 32hours. Half the tank and down to 16hours.