Re: Back of an envelope calculations
And if you go for some nice deep cycle car or truck batteries instead of the much smaller UPS batteries you absolutely phenomenal capacity.
A lead acid battery rated at 300 amps (not continuous) equates to 3.6kW for a single battery. And at lower power levels you'd get incredible duration.
I've got a small car battery dedicated to a 1.5kW inverter for emergencies. A friend had a black out a couple of weeks ago and it kept their TV and Playstation going for about a day before they got power back. The voltage afterwards was still 12.5v which is roughly 50%.