1.) check your battery health annually and replace bi-annually. I don't care about the battery quality, an always-online UPS is very hard on lead-based batteries. they're float charged basically all the time, and deep discharged during outages. if you're in a power failure prone area (i.e. more than one per year), invest in a generator too in order to avoid stressing the batteries with full discharges.
2.) check the battery float voltage with an actual volt meter to make sure the UPS is calibrated correctly. APC UPS's in particular, prior to and post the Schneider Electric buyout, had a lot of really poor cost-savings decisions applied to their enginnering. this included using a carbon film resistor-based voltage divider to measure the battery voltage on much (or all) of their Back-UPS and Smart-UPS range. if you don't know anything about resistor technology, carbon film resistors (especially cheap ones!) change in value due to temperature, humidity, and age, usually drifting up in resistance. this is a bad thing when you need a stable voltage reading...
oh and on APC's cost cutting measures; there's the fun time they stopped using nickel plating on the bus bars in their Symmetra UPS line. they switched to tin plating instead. apparently none of them had heard of tin whiskers. :)