Same problem with two identical systems: iMac21.5 OS X 10.6.2, Cyberpower CP825AVRLCD. Several times a day, both Macs display a spurious warning saying running on battery power. Energy Saver status is displayed on desktop and shows 100%. I also checked the UPS internal log (using a PC) and no power outages are reported.

This is not a big problem, but it is annoying. In fairness, the UPS works fine supplying regulated AC power and battery power. Depending on screen brightness, I can get at least 15 minutes battery power, up to probably over a half hour.

I've contacted Cyberpower ( twice now (Dec 2009), and no reply in over week.