A UPS [Uninterruptible Power Supply] uses one or more batteries that supply electricity to a PC or other electrical/electronic device(s) if/when there's a power outage. The basic idea with a PC is it gives you time to save your work and shut down gracefully, and they're also handy for brief power interruptions, e.g., when the lights flicker, so the PC keeps running rather than shuts down.
One problem however is that there's no great way to judge if the battery [or batteries] in a UPS are still good. In my case I use the CyberPower app on this PC, and checking the app after a couple of very brief outages -- 6 & 3 seconds per the in-app log -- the batteries were down to 40%! Based on the measured load the app estimated that I'd have ~45 minutes if the batteries were fully charged & in good shape. It was a lucky power outage BTW, since the extended warranty was up next month. The app's self test Did Not show anything wrong, so it's obviously useless in this case.
So, rather than wait for an outage, &/or if you don't have/use a monitoring app like CyberPower's PowerPanel Personal, it might be a good idea to, with the PC [or whatever] running, unplug the UPS from the wall and see how long it lasts, making sure the battery's still good. If you don't want to risk running Windows when it does shut off, boot to a USB stick for backup software or similar.
On a quick note, the latest PowerPanel Personal download is here -- checking for updates in-app did not show there was a newer version, and it had to be uninstalled first before the newer version would install.
cyberpowersystems[.]com/products/software/power-panel-personal/