As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEN - EEL - DURING 4-DAY CHECK OPERATIONAL TEST OF EMERGENCY LIGHT SYSTEM RECEIVED A LT OVERWING EMERGENCY POWER SUPPLY UNIT BATTERY FAULT. MAINTENANCE REMOVED AND REPLACED BATTERY PACK IN THE LT OVERWING EMERGENCY POWER SUPPLY UNIT (11WL), OPERATIONAL CHECK WAS GOOD.