I don't quite understand. If I have a power outage for four hours, I'm going to want my VorTech running the full period. Once power is restored, it should recharge the battery again. Obviously like any UPS, the battery will have a specific lifespan.
A local club member had a power outage last Sunday. He called me up to see what I'd suggest, and I told him to run to Home Depot's Tool Rental and get a generator in case he was without power for the night. He rented it for $36 for a 24 hour period. About four hours later, power was restored, but his reef was safe. Best $36 he ever spent, imho. It cost him less than a new coral, and his livestock was safe.
I like the VorTech option for those that can't be there to install a generator right as it happens. If it was a long term problem, I'd assume it would be best to move the VorTech closer to the surface to venturi in a little air into the flow. Would you agree, Andy?