So now you need to test them regularly. And order new ones when they're not holding a charge any more. Then power down the server, unplug it, pull the UPS out, swap batteries, etc.
Then even when I think I've got the UPS automatic shutdown scripts and drivers finally working just right under linux, a routine version upgrade breaks it all for some reason and I'm spending another 30 minutes reading through obscure docs and running tests until it works again.