POWER SUPPLY CONTROL DEVICE, POWER SUPPLY CONTROL METHOD, AND STORAGE MEDIUM

A power supply control device includes: a controller configured to perform a diagnosis of a degree of deterioration of a backup power supply that supplies electric power to a load of a vehicle when a main power supply that supplies electric power to the load fails. The controller is configured to start the diagnosis before a user gets in the vehicle, when detecting an occurrence of an event indicating that the user is to get in the vehicle.