Battery system

A battery system, comprising:

• a battery unit that comprises a plurality of secondary batteries connected in series;
• a positive electrode output terminal that connects a positive electrode of the battery unit and an external load;
• a negative electrode output terminal that connects a negative electrode of the battery unit and the external load;
• a first contactor that is provided between the battery unit and the positive electrode output terminal and that comprises a positive electrode terminal and a negative electrode terminal;
• a second contactor that is provided between the battery unit and the negative electrode output terminal and that comprises a positive electrode terminal and a negative electrode terminal;
• and
• a detector for detecting whether a direction of an electric current flowing between the battery unit and the external load is a discharge direction in which the battery unit discharges or a charge direction in which the battery unit is charged;
• and
• a control device, wherein
• the control device comprises:
• a disconnection event obtaining part that acquires that a disconnection event has occurred, the disconnection event that requires both the first contactor and the second contactor to be turned OFF so as to disconnect the battery unit and the external load;
• a determining part that determines whether a direction of the electric current when the disconnection event is generated is the discharge direction or the charge direction;
• and
• a disconnection control part that decides the order for turning OFF the first contactor and the second contactor based on a determined result of the determining part, and
• the disconnection control part is configured to preferentially turn OFF a contactor, through which a forward current flows from the positive electrode terminal to the negative electrode terminal, among the first contactor and the second contactor.