A battery changing system is provided to change the battery in an industrial truck, such as a fork lift truck, with a battery block that can be moved in the horizontal direction by a roller conveyor relative to a battery compartment of the industrial truck. The invention teaches that the battery in the industrial truck can be changed easily and economically by providing an external roller conveyor (5) that can be moved in the vertical direction. To change the battery, the roller conveyor (5) can be placed underneath a battery compartment (2) in the industrial truck that contains the battery (1) and then the roller conveyor (5) can be raised. A floor (7) of the battery compartment (2) of the industrial truck can be provided with at least one opening (8; 9) for receiving one or more rollers of the roller conveyor (5).