Energy storage device for charge equalisation of an energy storage arrangement, said energy storage arrangement comprising at least two lithium-ion storage modules (11a-11d) that are electrically connected in series, characterized in that the device for charge equalisation comprises: - a plurality of switching devices (211, 212, 213), each of which is coupled to the lithium-ion storage modules (11a-11d) of the energy storage arrangement, - a plurality of DC-DC voltage converters (241, 242, 243), each of which comprises a first side with a positive terminal and a negative terminal and a second side with a positive terminal and a negative terminal, wherein the first side of each of the DC-DC voltage converters can be coupled to each of the lithium-ions storage modules (11a-11d) via a corresponding switching device of the plurality of switching devices (211, 212, 213) that is associated with the respective DC-DC voltage converter, and the second side of each of the DC-DC voltage converters is coupled to the external terminals (17a, 17b) of the series circuit, - a control device for monitoring parameters of the lithium-ion storage modules (11a-11d) and for controlling the switching devices (211, 212, 213) and the DC-DC voltage converters (241, 242, 243), wherein the entirety of the series-connected lithium-ion storage modules of the energy storage arrangement is provided for intermediate storage of charge for the charge equalisation between the lithium-ion storage modules, the control device controlling the charging process and/or discharging process of the energy storage arrangement based on storage capacity values of the respective lithium-ion storage modules (11a, 11b, 11c, 11d), wherein a positive terminal of each of the lithium-ion storage modules can be coupled to the positive terminal of the first side of each of the DC-DC voltage converters in each case via a first switch, associated with the respective lithium-ion storage module, of this corresponding switching device, and a negative terminal of each of the lithium-ion storage modules can be coupled to the negative terminal of the first side of this same DC-DC voltage converter in each case via a second switch, associated with the respective lithium-ion storage module, of the corresponding switching device. - a plurality of switching devices (211, 212, 213), each of which is coupled to the lithium-ion storage modules (11a-11d) of the energy storage arrangement, - a plurality of DC-DC voltage converters (241, 242, 243), each of which comprises a first side with a positive terminal and a negative terminal and a second side with a positive terminal and a negative terminal, wherein the first side of each of the DC-DC voltage converters can be coupled to each of the lithium-ions storage modules (11a-11d) via a corresponding switching device of the plurality of switching devices (211, 212, 213) that is associated with the respective DC-DC voltage converter, and the second side of each of the DC-DC voltage converters is coupled to the external terminals (17a, 17b) of the series circuit, - a control device for monitoring parameters of the lithium-ion storage modules (11a-11d) and for controlling the switching devices (211, 212, 213) and the DC-DC voltage converters (241, 242, 243), wherein the entirety of the series-connected lithium-ion storage modules of the energy storage arrangement is provided for intermediate storage of charge for the charge equalisation between the lithium-ion storage modules, the control device controlling the charging process and/or discharging process of the energy storage arrangement based on storage capacity values of the respective lithium-ion storage modules (11a, 11b, 11c, 11d),