Want something cheaper, designed to work say…20 years without much maintenance and little loss in efficiency?
Use a Flywheel UPS!
The article says the upfront is a little more, but flywheel-based can save millions for some data centers in reduced energy costs. A 600-pound spinning slab will keep going for awhile without too much energy input.
Of course, it is only really helpful for the 15-45 seconds it takes for your generators to kick over.