An emergency power supply device is provided to supply emergency power to a direct voltage circuit. The direct voltage circuit has a first potential tap and a second potential tap, comprising an energy storage unit. The energy storage unit has a plus pole and a minus pole, and one of the poles is connected to the first potential tap via a first connection. The other pole is connected to the second potential tap via a second connection. At least one of the connections has a directional electric current meter and at least one of the connections has an interrupter. The directional electric current meter can measure a flow of charging current. The interrupter can prevent a flow of charging current, and the interrupter can be controlled as a function of the flow of charging current that has been measured.