What was found
WHILE AT GATE GROUND POWER WAS DISCONNECTED FROM AIRCRAFT AND EMERGENCY LIGHTS ILLUMINATED FOR 10 MINUTES. (NOTED BY FLIGHT ATTENDANT) FLIGHT ATTENDANT ATTEMPTED TO TURN LIGHTS OFF BY TURNING ON THE GROUND POWER SERVICE BUS, BUT EMERGENCY LIGHTS WOULD NOT EXTINGUISH UNTIL GROUND POWER WAS RESTORED. BATTERIES WOULD REQUIRE A 16 HOUR CHARGE TO RESTORE VOLTAGE CAPACITY SO MAINTENANCE REPLACED ALL 9 BATTERY PACKS IAW T/C A1C33005. SYSTEM OPERATIONALLY CHECKED GOOD.