Power Supply Control Method and Power Supply Control Device

A power supply control device includes a high-power battery, a low-power battery, a relay that electrically connects the high-power battery and the low-power battery, a power supply switch, and a controller that controls an on/off state of the relay. When a power supply state is a state in which power is supplied from the high-power battery to the low-power battery with the relay therebetween, if the controller receives a first signal, the controller switches the relay from an on state to an off state, and then inhibits the relay from switching from the off state to the on state.