As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: DURING SYSTEM TEST OF THE EMERGENCY POWER SUPPLY UNITS A BATTERY FAULT DISPLAYED FOR EMERGENCY POWER SUPPLY UNIT 12WL. MAINTENANCE REPLACED THE BATTERY FOR EMERGENCY POWER SUPPLY UNIT 12WL AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 33-51-38.