if you go to APC's site, you can plug in the size of the UPS and the load... you don't need to have lights (unless you're a reefkeeper, and if so, well, i'm not sure what to do; reef lights would blow through a UPS pretty quickly).
filter is about all; water keeps heat pretty effectively, especially if you have a full glass cover. i think that some of my bigger UPS's could probably keep a filter going for 2-3h.
of course, it would be beeping all the time, driving me crazy
yes, the batteries recharge. every so often it'll hum, and click as it tests itself.
check out the site i listed for the best price really.