Try shaking the battery...if you hear any rattling...it is junk.
We have about 100 UPS units where I work and I have some that the batteries are over 3 years old and work fine and others that seem to fail every few months.
I take apart all the old/defective units and salvage everything I can.
Lots of nice FET's. relays. connectors, heavy-duty power cord, switches, etc inside.
The transformer is not very useful unless you want to rewind it or salvage the copper wire from it.