As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: EMERGENCY POWER SUPPLY UNIT 15WL FAULT FOUND DURING TESTING OF THE EMERGENCY POWER SUPPLY UNITS. MAINTENANCE REPLACED EMERGENCY POWER SUPPLY UNIT 15WL BATTERY AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 33-51-38.