I have a Cyberpower CP1500PFCLCD ups. On a couple of different occasions I've had the ups seem to lock up and the devices connected to it powered off. The display showed that the battery was full. Nothing looked odd. However, I couldn't seem to turn it off by holding the power button. The way I was able to turn it off, was to unplug it and then hold the power button. It didn't beep, the display just turned off. Then I plugged it back in and turned it on normally. When it came back on the battery icon showed it was completely drained. My questions are, is the battery just finally worn out or is this a problem with the unit itself? Also, what is the part number for new batteries for this? I can believe the batteries are worn out because I've had this unit for 6 years, but I wouldn't think I would get this behavior from worn out batteries.