You'd have to get the mother of all power inverters to run a heater. The little ones are usually for running a laptop, or maybe a portable TV, say 30 watts. Even a small heater is going to pull 1000 watts. You can probably get a 1000 watt power inverter, the guys that have the car stereos that you can hear a half mile away use them. So going to a stereo shop is the place to start. But it's gonna be expensive.

Then we come to the battery system, for long term demand, I think a 12V car battery is good for maybe 4 Amps (call it 50 Watts/battery), so you'd need 20 car batteries to provide 1000 Watts of power. And that's assuming that your power inverter is 100% effiecient at converting the power. Its not! So call it 40 car batteries.

You might be able to do it with less if you're looking for only a short amount of time... but if your power is only out for a short time you wouldn't need a heater anyway. <img src="images/graemlins/confused.gif" alt="" /> I don't think its gonna be very feasible.