Energy storage system with implemented regulating algorithm and method for controlling the charge levels of its elements

The system has a change-over switch for removing a storage element out of the series arrangement, and for bridging the removed storage element. A separation switch is provided for removing the storage element out of the series arrangement, and a bypass switch for bypassing the removed storage element. The number of series-connected storage elements is varied by shifting change-over switch between the branch containing storage element and bypass branch, or by shifting the separation and bypass switches between the ON and OFF states. Independent claims are included for the following: (1) method for controlling charging state of storage element of energy storage system; and (2) use of energy storage system.