Normally, I just replace the batteries in mine as well. I used to go to Batteries-Plus for the replacements. You can bring your old unit in and they'll even pull the old battery out, show you which replacement you need and put the new one in for you (on a slow day). These days, I go to a local electronics store (the local competition for Graybar) and grab the replacements. The local guys are cheaper, but harder to find and further away.
For a typical 1000 kva UPS I'd use on a desktop, the replacement batteries are about $60 vs $200 for a new replacement.
As an added insurance policy against surges, I also use a separate surge suppressor (Tripp Lite TLP1208SAT) that cuts the power when used up.