UPS power system cannot detect battery

This can be caused by a drained battery, faulty power connections, or an internal hardware fault. How to Fix It: Ensure the UPS is plugged into a functional power outlet. Test the outlet with another device to confirm. A “battery not detected” error doesn't automatically signify the end of your UPS. That could clear up any short-term errors or glitches preventing it from detecting the battery. You could try updating the UPS firmware (if you can get hold of the latest version) but my experience is that this continues to happen even with the latest firmware installed. [pdf]