As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING PERIODIC SERVICE CHECK AFT EMERGENCY POWER SUPPLY UNIT FAILED THE CIDS SYSTEM CHECK. MAINTENANCE REPLACED THE AFT EMERGENCY POWER SUPPLY UNIT (AALA202304188452) AND BATTERY (AALA202304188029) PER AMM 33-51-38. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.