On-board unit, configured to determine the position of a vehicle in regular intervals and provide this position data to a central office for billing, the on-board unit comprising a system for deep discharge protection of a chargeable battery, the system comprises: a chargeable battery, which is configured to provide energy to a system, when operation of the on-board unit is needed and no other energy source is available; a battery charging unit with an internal switch, wherein the battery charging unit is coupled to the chargeable battery and is configured to charge the chargeable battery and wherein the battery charging unit is coupled between an output of the chargeable battery and a first terminal for a first potential; a deep discharge protection unit, which is configured to monitor a voltage of the chargeable battery and disconnect the chargeable battery from the system, when the battery voltage is lower than a given threshold voltage; and a transport mode unit, which is coupled between the deep discharge protection unit and the first terminal and which is configured to trigger an opening of the internal switch of the battery charging unit, wherein the chargeable battery is disconnected from the system when the at least one internal switch is opened; the system being configured to send a first transport signal to the transport mode unit after inserting the chargeable battery in the on-board unit and the transport mode unit being configured to send a second signal to the deep discharge protection unit, which results in a third signal being sent by the deep discharge protection unit to the charging unit, and the third signal causes the charging unit to decouple the chargeable battery from the system by opening the internal switch, wherein the internal switch is closed and the chargeable battery is coupled to the system again, when the on-board unit is mounted in a vehicle and the first terminal is coupled to a vehicle battery. a chargeable battery, which is configured to provide energy to a system, when operation of the on-board unit is needed and no other energy source is available; a battery charging unit with an internal switch, wherein the battery charging unit is coupled to the chargeable battery and is configured to charge the chargeable battery and wherein the battery charging unit is coupled between an output of the chargeable battery and a first terminal for a first potential; a deep discharge protection unit, which is configured to monitor a voltage of the chargeable battery and disconnect the chargeable battery from the system, when the battery voltage is lower than a given threshold voltage; and a transport mode unit, which is coupled between the deep discharge protection unit and the first terminal and which is configured to trigger an opening of the internal switch of the battery charging unit, wherein the chargeable battery is disconnected from the system when the at least one internal switch is opened; the system being configured to send a first transport signal to the transport mode unit after inserting the chargeable battery in the on-board unit and the transport mode unit being configured to send a second signal to the deep discharge protection unit, which results in a third signal being sent by the deep discharge protection unit to the charging unit, and the third signal causes the charging unit to decouple the chargeable battery from the system by opening the internal switch, wherein the internal switch is closed and the chargeable battery is coupled to the system again, when the on-board unit is mounted in a vehicle and the first terminal is coupled to a vehicle battery.