Get a portable generator! One that puts OUT more "juice" that your batteries sent off to the furnace. There are many that run quietly and are fuel mizers.
My own Honda 2000 watt model SAYS it can run for 6 hrs without refilling...but one winter here at home I ran it on the lower output side ( no idea what watts it was putting out) but it ran my VCR and my 60" flat screen TV for 8 hours and that when I shut it off to refuel because I didnt want to have to do it in the darkness. ( Storm put heavy ice on everything and killed the electricity feed)
Find out how many watts / amps your furnace takes and go accordingly
