Why does my Classic Mini start in DAB mode when it is running on battery power?

When you switch off your Classic Mini while it is running on battery power, the device switches off completely and the time settings are lost.
To restore this data, the Classic Mini starts in DAB mode.

This behavior is limited to when the Classic Mini is running on battery power.

When the device is connected to a charger, it starts up with the last source played, as the time data is retained in standby mode.