The invention relates to a method for charging or discharging an energy store (2) with at least one cell block (20) consisting of multiple series-connected battery cells (3-7) by means of a series charging current (IO) flowing through all battery cells (3-7), wherein at least some of the battery cells (3-7) can have different capacitances (CN).
In order to permit a reliable and quick charging of energy stores, the invention proposes measuring the capacitances (CN) of the N battery cells of the cell block at regular time intervals, and determining a maximum charging current for each battery cell based on the measured capacitances and a predefined C-factor (ratio of the maximum charging current IN;max to the capacitance CN) for each battery cell. With these maximum charging currents, the battery cells are then simultaneously charged during a charging time t (t≤1/C) predefined by the C-factor. In addition, the battery cells with a maximum charging current that corresponds to the series charging current IO are only charged by the series charging current; the battery cells with a maximum charging current IN;max that is greater than the series charging current are simultaneously charged by the series charging current and by the auxiliary charging currents IN that can be removed from the cell block, for which IN=IN;max−IO; and the battery cells with a maximum charging current IN;max that is lower than the series charging current Io are charged by the series charging current, wherein, simultaneously, the currents Io−IN;max exceeding the maximum charging currents IN;max are supplied to the cell block as discharging currents.