DIAGNOSTIC DEVICE, DIAGNOSTIC METHOD, DIAGNOSTIC SYSTEM, AND PROGRAM

A diagnostic device () includes: an acquisition unit () that acquires first charging information including a first detected value detected by an external charger () during charging of a battery mounted in a vehicle () and second charging information including a second detected value detected by the vehicle; and a deterioration estimation unit () that estimates a deterioration degree that indicates a degree of deterioration of the battery on the basis of the first charging information and the second charging information.