Method and system for balancing electrical energy storage cells

The present invention relates to a system (13) for charge balancing over a plurality of rechargeable energy storage devices (12) coupled in series, said system (13) comprising a plurality of balancing units (15) each assigned to one of the rechargeable energy storage devices (12), an AC signal generator (14) for providing an AC signal to the plurality of balancing units (15), and a capacitive coupling between the AC signal generator (14) and each of the plurality of balancing units (15) for common mode blocking.