As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT IN BASE MAINTENANCE: DURING BITE CHECK OF THE EMERGENCY POWER SUPPLY UNITS, EMERGENCY POWER SUPPLY UNIT 13WL BATTERY FAULT DISPLAYED. MAINTENANCE REPLACED THE BATTERY FOR EMERGENCY POWER SUPPLY UNIT 13WL PER AMM 33-51-38 AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.