A mobile electronic device comprising an internal circuit and a battery compartment having an entrance and an exit. The battery compartment comprises a first conductor and a second conduct at the inner side of the battery compartment. The first conductor comprises at least two conductive contacts electrically connected to the internal circuit and having a distance from each other in the direction from the battery entrance to the battery exit so that, while a backup battery is sliding into the battery compartment from the battery entrance and pushing out a current battery through the battery exit, the first conductor may maintain electrical connection with conductive belt of the current battery and/or the backup battery. The structure of the second conductor is similar that of the first conductor and may maintain electrical connection with conductive belt of the current battery and/or the backup battery.