Also check the model and serial # of that UPS. There was a recall 10+ yrs ago for it:
https://www.apc.com/site/press_cent...two-uninterruptible-power-supply-models/

A quick check would be if the case is white, then it is probably of that vintage. Probably time to get rid of it anyway and get a new one (preferably with pure sine wave output which handles electrical spikes and dips that some generators put out for electricity).