At some point ( 2 to 5 years), the batteries in your APC UPS unit are going to go bad. Once they are bad, you may see a red bad battery LED, the UPS may shutdown, the batteries may get very hot and start swelling, etc. Using the Powerchute software, you may also notice that the battery runtime is very low, when compared with a normal reading. As an example, our SU 2200NET UPS has a runtime of about 20 minutes at 50% load. One day, it started showing a runtime of 6 minutes. I did a load test and the UPS completely shutdown after 2 minutes.
The fix was to install new batteries. APC wants you to purchase their brand of batteries, but they are very expensive. After-market batteries are very inexpensive and there are lots of new units listed on Ebay. After you replace the batteries, you would expect the runtime to be back up to normal values. That might not always be the case. For my new batteries, the load test still only resulted in an operating time of 2 minutes. If you still see a low run time value with new batteries, then you may have to do some internal programming on the UPS so that it knows that new batteries are iustalled.
Send me an email or give me a call and I can tell you about the simple procedure for getting the newly installed batteries to have the correct run time.