Often these UPS are advertised as "Not Working" but are in very good order apart from poorly batteries. Some batteries show the full voltage under no load conditions (after charging for a long time) but the voltage collapses when a small load is applied. I use a 12V bulb (a car bulb) to load the battery and then measure the voltage.
This APS unit was a bargain because all I had to do was to replace one of the two 12V batteries and it worked perfectly. The electronics of the unit are first class so they seldom go wrong.
Some units are dispatched without batteries. If you buy one of these then make sure that the battery cables are included with the unit even if the batteries are not.