A battery management system includes a first battery pack which supplies power to a load, a first ground unit which is connected between a first relay which is connected to the first battery pack to connect and disconnect power supply of the battery pack and the first battery pack, a second battery pack which supplies power to a load, a second ground unit which is connected between a second relay which is connected to the second battery pack to connect and disconnect power supply of the battery pack and the second battery pack and a voltage measuring unit which measures voltages of both ends of the first relay and voltages of both ends of the second relay.