Energy storage device (1), with: a plurality of parallel-connected power supply branches (Z), each coupled between an output terminal (1a, 1b, 1c) and a reference potential rail (4), wherein each of the power supply branches (Z) has a plurality of series-connected
energy storage modules (3), each comprising: an
energy storage cell module (5) which has at least one
energy storage cell (5a, 5k), a
coupling device (7) with
coupling elements (7a, 7d; 7b, 7c) which are designed to selectively connect the energy
storage cell module (5) to the respective
energy supply branch (Z) or to bypass it in the respective
energy supply branch (Z), and a
current sensor device (8, 9a, 9b) which is connected in series to the at least one energy
storage cell (5a, 5k) and which is designed to measure a current through the energy
storage cell module (5) and to output it as a module current measurement
signal; and a
control unit (6) which is coupled to each of the
current sensor devices (8, 9a, 9b) and which is designed to process the module current measurement signals of the
current sensor devices (8, 9a, 9b), wherein the
control unit (6) is further designed to control the
coupling devices (7) of the energy storage modules (3) either in pulse-width modulated operation or in
continuous current operation, and to average only the module current measurement signals of the current sensor devices (8, 9a, 9b) of those energy storage modules (3) which are controlled in
continuous current operation to form a
branch current measurement
signal.