Not long at all. The heater is a major drain on the battery. I have a Pacifica PHEV, when I run the heater the engine almost always turns on. You’ll see a huge difference between warm and cold temperatures. Engine usually needs to run a bit to get heat.My understanding is the electrical engine runs the climate when the ICE is off? If that is that case would it be possible while camping, to run the heater in the vehicle for some extended period of time? Any guesses how long it would run like that with a full battery charge? Is the heater able to provide warm air without the ICE running to heat up the coolant?