Per nesesu:
At work we had a very large UPS that used 600V of gel-cell 12V
batteries each about the size of a largish car battery. In the 15
years or so that it was in use, there were, perhaps, 5 power failures
and the UPS failed every time even though all the routine maintenance
and testing was observed. Other than the first time when it was only a
month or so old and the inverter blew up [linerally] all the rest of
the failures were due to battery failure.

This begs a question that's been bugging me for years: why
doesn't somebody make a UPS that hooks up to a 12-v non-vented
automobile battery?

Automobile batteries are available at many different
price/quality points, they're pretty much a universal standard,
the capacity is there in spades, public knowledge about
maintaining/replacing them is widespread, and push-comes-to-shove
in an extended outage, the battery in somebody's car can be
swapped in for a few more hours working time.

I guess there has tb a reason... but what?
--
PeteCresswell