Batteries can also be maintained by an inverter/charger, much like a live aboard boat. Many people that work at home with computers have such systems that can run for a day or two.
The minute the power goes off your life has changed.
Just because you still might be able to use your computer for a couple of days after the power goes off doesn’t mean you still have anything to use it for.
A day or two?
YGBSM.
I just checked the box my UPS came in, and the largest model listed shows 70 minutes of runtime for a computer.
That's assuming your ISP is still alive.