The paper presents a high efficient charge equalizing circuit for series connected battery cells using the inductor voltage second balance and the transformer coupling principle. The proposed circuit is motivated from a general buck-boost converter with a multi-winding transformer coupling, and operates under zero voltage switching (ZVS) and zero current switching (ZCS) condition, which is achieved by only one single resonant circuitry through a multi-winding transformer coupling effect. In this paper, the principle of operation and design consideration is explained detail. To verify the proposed circuit, prototype board is built and experimented. Based on the multi-winding transformer coupling and ZVZCS switching operation, the proposed circuit provides a fast balancing speed and a high switching frequency operation, which result in a cost, size and weight reduction.