My UPS is dead :*(

[#1]

I've been using a freecycled UPS for the last couple of years. Nice and reliable bit of kit never let me down, saved me from sudden power cuts etc...
Today my missus unplugs it which wouldn't normally be a problem.. except it let out two beeps and turned off  The result was naturally a loss of anything open / running and me then trying to resurrect the damn thing.
It eventually came back to life but won't power anything without faulting. If I unplug the monitor / computer from it and then turn off the power to it, it continues running happily. Plug the computer / monitor back into it and it faults again with a red light and a constant flat-lining tone.
It's a Powerware 5110:

Anyone else had this bit of kit / problem?

[#2]

Battery has probably got too weak to power whatever you have hooked up to it.
It's quite common for a cell to die in the SLA

[#3]

The Battery's should be changed once every 5 years of use at least.

[#4]

My UPS stopped working recently - I now have a new battery in the UPS and it's fine again (also gained a very useful doorstop!).

[#5]

I may well give that a try then when I can afford to! It's sat under the desk at the moment lol. Not in a hurry to dispose of it so one day it may see service again..
Considering it was a freebie from a local freecycler it's done me well for the last two years!