Power failure alarm indicated

The vent can work off of both AC or Battery. Check the AC adapter. If it is not providing adequate power to charge the battery, then the battery is actually being used to power the vent. There is a RED light to indicate when the battery is 5 hrs to depletion. Also check the battery. There is a manual in the Database with schematic of the electronics for the vent. This should help with troubleshooting. Good Luck.