An electrical energy supply device having a plurality of usage units, each usage unit being adapted to generate or to buffer electrical energy. The usage units in the energy supply device are divided up into strands and each strand is adapted to generate a summed voltage by a series circuit of the usage units, and each strand end is connected across a respective switching unit to a busbar assembly and within each strand a bridging circuit is provided for each usage unit and a control device is adapted to identify a defective usage unit in one of the strands and to then galvanically separate the strand by its switching units from the busbar assembly.