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.
Webasto would like to have a word. "..can operate for up to 22 hours on less than one gallon of fuel.."
https://www.webasto.com/en-us/choose-vehicle-solution/oil-an...
Just as a point of contention. Its hard to find an EV that is only gonna pull 1000w using the heater.
My EV doesn't have a heatpump and the resistive heating pulls up to 8KW warming up the cabin on a cold day.
I keep a 12v heated blanket around to save power. (no heated seats/steering wheel)
Heated seats are where the real power savings come in.