Abstract: A device (3) and a method for equalizing the voltage of an energy-storage element (4) are provided herein. The device (3) comprises at least one transformer (36) and at least one bi-directional DC/AC converter circuit (35). Each transformer (36) comprises at least one equalizing winding (30) and at least one transforming winding (26,27). The DC terminals of each DC/AC converter circuit (35) is adapted to connect to a positive terminal (41) and a negative terminal (42) of the energy-storage element (4), and the AC terminals thereoft is connected with the transforming winding (26,27) of the transformer (36).