Realistically there are only 3 ways to do a power backup,
1- get 12 volt motors and 12 volt batteries,use a normally open contact to energize the dc
motors when line power fails.
2- get a LARGE UPS with a 120 volt inverter build in
3- get a generator with a transfer switch
I use the 3rd option as I consider it to be by far the best.
I am an electrician by trade so I did it for a much lower cost then is available to most however it is not as expensive as replacing a well stocked tank.
The advantages are as follows
1/ can run all tank equipment lights,heaters,pumps
2/ if generator is running on natural gas it will never run out of fuel
3/ can run house furnace and or a/c to maintain house temp normal
4/ wife not pi**ed at you since only thing working in the house is your tank
I run a 6.5 KW gen on gas and it will handle any emergency, the gen is around 1,000 and the transfer switch another 600 and finding a electrician friend should not be hard
As far as the tank ya I would cycle it again