Per PeterD:
Automotive batteries are not well suited to long, continous drains
that the UPS would require. Using a deep cycle battery (such as a
trolling battery, or an RV battery, would work, but not optimal.)

Is that to say with the first power outage and running the
battery to near-exhaustion (assuming there is a means to control
how far down it goes) that the battery would be damaged?
--
PeteCresswell