At that temperature, a battery's voltage is almost cut in half, so you would probably have to get a battery blanket. I think it is something similar to a NOS bottle heater, or a block heater. I'd think you'd have a block heater as well out there as well, so you could just adapt a heat blaket onto the wiring going to the block heater. Something like that...I dunno. Maybe you can adapt that idea and Mcguyver something? I am pretty sure they make something like this somewhere.

Hope this helps ya,

Mav

 

They do make "battery blankets" but they usually tap into 110V household current. (you plug them in like a block heater).

I would NOT reccomend using some form of a 12V battery blanket, as you could drain the battery.

Also...the trunk being colder than the engine compartment theory doesn't really hold water (or freeze water to butcher the anology).

When you start your car in the morning, your battery is going to be -30. It doesn't matter if it is in the engine compartment or in the passenger compartment, it is going to be damn near ambient tempature. The inside of the car should be a tad more insulated from the cold vs the engine compartment, but the engine compartment has a radiant heat source (the engine) for a tad bit after being shut off. In the end, it should equal out. You heat up the passenger compartment just like you heat up your engine bay. In fact, I'm willing to bet in -30 degree temps, the battery will be warmer IN the car while driving vs in the engine compartment while driving. Besides...once the car is started...the battery can just about freeze solid, the alternator will keep the engine runnin.