There isn't a real great way to test those batteries with out some kind of equipment that can discharge them at the prescribed rate. Usually those batteries will get to 12.5-13.0 volts or they won't, when they won't you can call them bad.

You need to come up with a schedule for battery replacement for power supplies. Waiting until the batteries fail can cause problems. Sometimes the batteries swell up and won't come out of the units, or they melt down. My APC unit was telling me the battery was bad and I let it go a few days, battery goo all over in the entertainment cabinet and a pretty wicked smell.