As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING CIDS OPERATIONAL TEST OF THE EMERGENCY POWER SUPPLY UNITS, FAULT MESSAGE FOR LEFT OVERWING EMERGENCY POWER SUPPLY UNIT DISPLAYED. REPLACED EMERGENCY POWER SUPPLY UNIT (AALA202307115603) AND BATTERY AALA202307110838) PER AMM 33-51-38. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.