Why is my APC Back-UPS emitting a single beep every 5 seconds?
Back-UPS, Back-UPS PRO
The Back-UPS product has transferred to battery power due to a low voltage condition at the wall. The Back-UPS has remained Onbattery until its runtime was totally exhausted, however, there was still enough voltage present at the wall to trickle charge the battery.
This is considered to be a normal operating state.
When the voltage returns to normal the Back-UPS will wake up and restore power to the battery outlets.