I wouldn't run one off a car battery all night away from home because
they consume a fair amount of current internally and you might not be
able to start the engine in the morning.

-jsw

Right. I know mine is sucking power even when switched off. Where we're going I need to leave the car a fair distance from the tent and will be using a spare battery, mostly without the inverter attached. Still have to work out options for recharging in the morning...