Series-connected lithium batteries can be charged in pack mode that is most widely used in lithium battery application field. But pack charging mode will lead to cell unbalanced charging because of cell differences among series-connected batteries in electrochemical characteristic. On the other hand, the cell charging mode can avoid the imbalance problem by charging each cell independently as a result of reducing the charge efficiency and raising the cost. In this paper, a novel balancing strategy is proposed with pack charging mode and cell charging mode mixed to implement balancing algorithm. The proposed balancing system is based on the distributed power supply technology and the power bus technology. A DC voltage bus and an AC quasi-square wave voltage bus are built by relevant converters. The proposed method aims to solve the problem of charge imbalance with simple balancing algorithm and make the charge efficiency stay as high as possible.