As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: EMERGENCY POWER SUPPLY UNIT 13WL BATTERY FAULT MESSAGE DISPLAYED ON MCDU DURING THE TEST OF THE EMERGENCY LIGHT. MAINTENANCE RE-RACKED THE BATTERY FOR THE EMERGENCY POWER SUPPLY UNIT 13WL PER AMM 33-51-38. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED PER AMM 33-51-00.