Control device, battery unit, and work machine

This control device is for controlling a charging operation for a battery. The control device comprises: a first electrode that is electrically connected to a power unit and receives first power that is from the power unit as charging power for the battery; a second electrode that is provided so as to be electrically connectable to a prescribed power source and can receive second power that is from the prescribed power source as charging power for the battery; and a rectification element that is arranged on an electrical path that is between the first electrode and both the battery and the second electrode so as to allow passage of the first power to the battery from the power unit and to restrict passage of the second power to the power unit from the prescribed power source as electrically connected to the second electrode. As a result, the charging operation for the battery can be appropriately controlled.