I have two APC 2200's, and got my batteries from Jupiterbatteries.com.
When you replace UPS batteries, replace them with deep cycle AGM batteries. They will last WAY longer than the originals, have less of a chance of leaking, and have little chance of bulging. Jupiter has these. Make sure they are AGM!
I've got a couple of rackmount APC's on the way that need batteries, and I'm gonna order deep cycle AGM's from Jupiter for them.