CONTROL DEVICE, DIAGNOSIS SYSTEM, CONTROL METHOD, AND PROGRAM

A control device that controls charging/discharging of a secondary battery mounted on a vehicle includes: a detection unit configured to detect start of deriving of a deterioration state of the secondary battery; and a control unit configured to control charging/discharging of the secondary battery such that a charging rate of the secondary battery is equal to or higher than a first predetermined value and equal to or lower than a second predetermined value in a state in which the vehicle is parked and is connected to an external power supply in a case in which start of deriving of the deterioration state has been detected by the detection unit.