Some months ago my Tripp lite back up UPS failed. Turns out that the battery on it died and needed to be changed.
Getting the old battery out of the casing was a pain in the ass because it had swollen to a much larger size and it got stuck inside the device. It also leaked a bit, and that cause the plastic to melt together, not cool. Finally, this the UPS was out of warranty and we had to pay for the battery.
Anyway, the replacement battery once installed and configured has been working out well for us. I expect that it will last a few more years before it needs to be replaced again.
A UPS is not very cheap so if you have the ability to replace the batteries, then do so. It can save you a lot of money and work out just as good as new.