I have a Cyberpower 1000VA which I bought used on Facebook marketplace for $40. The original owner said he thought that the batter was dead and it just needed a new battery so I bought it off him and ordered a new battery for it. After trying the new battery the UPS still does not switch over the battery when I disconnect the power cord from the wall.

If I get an APC unit instead (more of them pop up for sale on the used market) can I use the battery I ordered for a similar sized APC unit?