A:Answer “Runtime” refers to the total amount of time the UPS can power your device during an outage—regardless of whether the device is actively in use or just in standby. So in the example you mentioned, the 51 minutes of runtime means the UPS kept the router powered for 51 minutes continuously, whether or not someone was making a phone call.
For your Xfinity Voice router, that runtime would cover both standby and active use, as long as the power draw stays consistent. Keep in mind that actual runtime can vary depending on the router’s power consumption and battery age.
I have a heavier load than most people, with two routers, a cable modem, and an 8-port switch. Even so, the APC BE600M1 UPS keeps my network running through outages lasting up to two hours for me. As the battery ages, that up time will drop.