In isolated instances, APC customers have observed a single beep being randomly emitted from their UPS
Back-UPS and Back-UPS PROEnvironment:
In the majority of these cases, it was determined the UPS had transferred to the On Battery State (powering the load from internal batteries) momentarily and returned to the Online State (utility power) before the On battery notification (4 beeps every 30 seconds) could be completed.Resolution:
The purpose of the On battery notification is to inform the customer when the UPS has sensed a power anomaly and has begun to power the connected equipment from it's internal batteries.
If a customer observes their UPS switching to the On Battery State frequently, an adjustment to the UPS thresholds for transfer may be required. Customers may reference the steps for adjustment of the UPS in their product's user manual