Didn't see this earlier. I used to use a Deep Cycle 12v battery and a 900watt inverter to run the fans on our insert. Back then we didn't have a furnace, the insert was our primary heat source. The deep cycle ran the fans about 12 hours. That was the longest outage where we used it, it may have gone even longer, I dunno.
Annnnnd...... it's out again. Went down around 1600.
I always wondered what it's like to live in Venezuela. Now I don't have to wonder any more.
EDIT: Just received an OEM robocall. Power surge demand fried a substation which caused a chain reaction that killed several transformers, which in turn, fried some lines. Was assured that "JCP&L is working feverishly" to restore power.