Those things are made so cheap that it doesn't even pay to replace the batteries. Once they start having problems it's time to replace. Nobody, including the manufacturer, supports them. Used to spend time prying swollen gel-cells out only to find that the thing cooked them when charging. Decided a long time ago, if the UPS doesn't work tell the customer that they have to replace it. Don't waste your time.
-Hal
The older APC's are indeed hard on batteries, and I've also dug my share of swollen cells from UPS cabinets. I have gone to the practice of shotgunning batteries on a 3-year schedule.
I can go 4-5 years between battery swaps on other brands. The last owners at my day-job went with Tripp-Lite, which haven't been as hard on batteries. The new owners like APC, so we'll see if their new models treat batteries nicer.
