An in vehicle device transfers connection information to a power management device, the connection information indicating whether the in-vehicle device can communicate with the power management device. The in-vehicle device either transfers condition information to the power management device, the condition information indicating that the in-vehicle device is ready for turning off, or sets the in-vehicle device to not communicate with the power management device when a predetermined condition is met, the predetermined condition indicative of an inability of the in-vehicle device to transfer information to the power management device. The power management device requests the connection information from the in-vehicle device and requests the condition information from the in-vehicle device. The power management device determines that the in-vehicle device is ready for turning off when both the connection information and the condition information have been received from the in-vehicle device, or no connection information has been received from the in-vehicle device because the in-vehicle device has been set to not communicate with the power management device.