What was found
IAH- MAINTENANCE, WHILE PERFORMING A SERVICE CHECK THE MECHANIC NOTED THAT THE MIDDLE CABIN EMERGENCY LIGHTS FAILED TO ILLUMINATE. IAH- MAINTENANCE REMOVED AND REPLACED THE RIGHT HAND MIDDLE EMERGENCY BATTERY PACK, PERFORMED A OPERATIONAL CHECK OF THE EMERGENCY LIGHTING SYSTEM, NO DEFECTS NOTED, AND, THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE