Normal mean time to failure is 3 to 5 years. My two year old (plus 3 months) did not reset on a power restoration. A power restoration is the severest load because in addition to the devices being powered, the UPS has to recharge the batteries. I reset it manually by unplugging the devices, turning on the UPS and reconnecting the devices on at a time. Not very handy if you are not around.
I have tested power interruption on a new, slightly larger UPS three times and the new one coasted through the tests.