UPS and heater(s)

I had another power outage last weekend (4+ hours), so I finally broke down
and bought a couple of refurbed UPSs. They should last a while as they are
36 amp hours each. The Goldfish tank only uses 24 watts (2 Fluval 304s), as
I won't connect the heater or lights. But I was wondering about the Tropical
tank, since batteries last exponentially longer under reduced load. Would I
not be better to have one 100 watt heater running twice as long, rather than
the normal two 100 watt heaters. In fact I was thinking about replacing the
two 100 watt heaters with a decent digital heater and leaving one of the 100
watt heaters in the tank as a backup. I would set the backup below the
threshold of the main heater (say 75°F) and connect it to the UPS. This way
the heater would not come on until the power had been off for a while.

Also do I need to connect the UGF filter to the UPS or can the bacteria
survive in the gravel for a while?