METHOD FOR OPERATING AN ENERGY STORAGE SYSTEM OF A WIND TURBINE, ENERGY STORAGE SYSTEM AND ENERGY STORAGE DEVICE

The method is for operating an energy storage system (200) which comprises an energy storage device (240) having a serial connection of energy storage cells (242). The energy storage system further comprises a plurality of contact points (244, 246, 248) across the serial connection for measuring a parameter (P) as well as a charging circuit (214) for charging the energy storage device. The method comprises a step of providing first information (I1) which is representative of an outcome of an operation performed on at least one measured value (M) of the parameter across at least one pair of contact points. In a further step, second information (I2) is provided which is representative of an outcome of an operation performed on at least one reference value (D) of the parameter across the at least one pair of contact points. The at least one reference value is the value of the parameter expected when the energy storage device is of a predefined type. Third information (I3) is determined depending on the first and the second information. The third information is representative of whether the energy storage system is of the predefined type. In a further step, operating information (OI_1, OI_2, OI_3) for the charging circuit is determined depending on the third information.