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?
I would advise that you go for V4 CPU instead. You get more cores, power consumption is lower and performance is better. You can find these CPUs on eBay shipped for about $50. The V4s I think are generally on the 14nm process whereas V3 on 32nm.