Just beware. I have an APC of a similar size. Probably not quite as nice but last time I replaced the batteries, it still said it had plenty left but couldn't sustain my server when I pulled the plug.
I have just replace 3 x APC UPS 1500 (Tower) today.. Same issue!.. Little power trip and the entire server shuts down and the UPS reboots... If you are brave, pull the mains power!
Either the UPS will kick over to run on battery OR turn off completely.
If it is stays on, you may notice it drains the battery very quickly.... from 100% to 20% in less than 30secs...
Another thing I noticed was, once you connect the AC the UPS will reboot/re-initialize, causing your equipment to either power cycle or stay off.
The toughest part of the day was lugging 6 x 22AH SLA batteries up the stairs to the comms rack/room. Despite the challenges, these are great UPS units, and it's worth noting that these 3 were still going strong after nine years with their original batteries!
i have 3 of those APC 1500VA sinewave jobs, one in the rack (main network, freenas box and NVR) , one on the HTPC and associated audio gear and one of the daily driver computer. the "unplug it" test works on them all but i time timed them, i just pull it for maybe 30 seconds with about 1/2 load.
but yeah new batteries for all of them is on the list. just been lazy as they are way overpowered for the load i have them hooked to.
anything worth doing is worth overdoing i figure.