APC consumer grade is junk, anything over 30 minutes and the mosfets burn out, and i doubt the batteries will last over a year or two because they don't cycle them and AGM/SLA batteries need to be cycled or left at a float voltage, they love to keep them at a cycle charge voltage and boil off all the electrolyte and then that causes the terminals to rot apart, or an internal failure due to acidic gas from the batteries. I take that back about just consumer grade, even APC rackmount/datacenter UPS's suck, I've seen the batteries blow up after a year and you couldn't even get the goddamn APC out of the rack it had expanded so much and remember another one quitting with a buzzing noise..
on the other hand, a pure sinewave inverter + external batteries and a transfer switch, costs a bit more but is much more reliable and the transfer time is 6ms or something when the inverter has a grid sync/lock, the lights don't even flicker... i use an inverter that runs on 40-60vdc, can use battery cables about 1/3rd the size of a 12v inverter. youd be surprised what you can find in used industrial/telco stuff that's perfectly fine and hardly been used if at all..
on the other hand, a pure sinewave inverter + external batteries and a transfer switch, costs a bit more but is much more reliable and the transfer time is 6ms or something when the inverter has a grid sync/lock, the lights don't even flicker... i use an inverter that runs on 40-60vdc, can use battery cables about 1/3rd the size of a 12v inverter. youd be surprised what you can find in used industrial/telco stuff that's perfectly fine and hardly been used if at all..