In this paper, the proposed charging system consists of step charging mode and time-sharing equalization charging mode. As $Delta$V=O point is detected, the proposed cut-off method will selectively cut off the only battery to reach the $Delta$V=O point, preventing serial-connected batteries from undercharging. In the start of each step, the equalization charging mode is performed to reduce the capacity difference among the batteries. Though it is added to simple circuit for selective cut-off, comparing with recently used step-charging method, this system can improve the life cycle of battery and charging efficiency, and be also very effective for preventing the batteries from overcharging and undercharging.