As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5909, STL TO IAH. DURING TEST THE EMERGENCY LIGHT ON THE LEFT SIDE NEXT TO THE OVERWING EXIT WAS FOUND TO BE INOP. MAINTENANCE SWAPPED EMERGENCY LIGHTS AND SLAVED IN A NEW BATTERY PACK FOR TROUBLESHOOTING WITH NO FIX. THE NR 5 INVERTER WAS THEN REPLACED AND THE EMERGENCY LIGHTS OPERATED NORMALLY.