As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: WHILE ACCOMPLISHING TASK CARD 26L00025010 STEP 11. D. MAINTENANCE PERFORMED OPERATIONAL TEST OF EMERGENCY LIGHTING SYSTEM PER AMM 33-51-00-710-001 AND THE OPERATIONAL TEST FAILED ON FLIGHT ATTENDANTS PANEL, A FAULT MESSAGE FOR THE EMERGENCY POWER SUPPLY UNIT BATTERY EXIT LEFT DISPLAYED. MAINTENANCE REPLACED THE BATTERY IN EMERGENCY POWER SUPPLY UNIT 11WL AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.