Cause : Control unit battery comes when the battery of the control unit is low or an issue with the backup battery that powers the control unit's memory during a power failure.

The fault code A5F4 in your ABB ACS880 drive indicates a Control Unit Battery Warning. This isn't a critical fault that immediately trips the drive, but it serves as a warning that the internal battery within the control unit might be nearing the end of its lifespan or malfunctioning.

1. Replace control unit battery.
2. This warning can be suppressed using parameter 31.40.