As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT ATTENDANTS REPORTED THAT THE CABIN WAS IN EMERGENCY ELECTRICAL CONFIGURATION, INCLUDING FLASHING EXIT SIGN LIGHTING, AT CRUISE. ALL COCKPIT INDICATIONS WERE NORMAL. REMOVED AND REPLACED EMERGENCY POWER SUPPLY UNIT 15WL BATTERY PER AMM 33-51-38.