UPS batteries are usually the lead-acid kind (like car batteries) and need to be replaced every 3-5 years. My UPS recently started complaining that the batteries just weren’t adequate anymore. The batteries were over 7 years old at that point. Looking around the net, I found an excellent small company called Jammin Works which sells very economically priced battery replacement kits for APC UPSes. I was able to get battery kits through them for less than half what a APC branded kit would cost. I got them all installed and they are working out great. (An initial problem I had with them turned out to be due to a loose connection when I installed one of the batteries.) You can often get used UPSes pretty cheap because people don’t want to pay for the branded replacement batteries, so you can often get a good deal on one and replace the batteries yourself for pretty cheap.
Once you’ve done the upgrade, what do you do with the old batteries? It’s ecologically unsound (and in some places illegal) to just dump them in the trash. I tried calling the county hazardous waste department for suggestions, but they only have occasional drop offs for that sort of thing. Finally I found some information that some stores will take old batteries for recycling. One of those was Sears Auto Centers, so I called up a nearby one and they said they’d take them. I drove up there to the battery center and they rolled up a cart and took them off of me for no charge. Nice.