> The blower motors are pretty power hungry, on the order of about 330 watts, give or take. For a 12V system that is about 30 amps, or about 2 hours of output from a typical deep cycle batter before you risk depleting it to the point of damage. An ~$300 12V Lifepo4 battery might get you 4 hours of runtime, but not much more than that.

This is 2-4 hours of run time though. My experience is that the blower turns on for a period and then off for a period. It would depend on your heat loss rate which is situation specific, but you can probably get significantly more than this in time coverage with the blower only running periodically.