The existing series-parallel switched-capacitor (SPSC) equalizers have a high voltage stress on switch, which reduces the reliability of the equalizer. To overcome this problem, an automatic voltage equalizer based on switched-capacitor for series-connected cells is proposed in this paper. In the proposed equalizer, the maximum voltage stress on switch is significantly reduced compared with existing SPSC equalizers, which improves the reliability of the equalizer. The proposed equalizer also shortens the length of equalization path between cells, which increases the equalization speed. The equalization speed of the proposed equalizer is analyzed in detail, and design considerations are proposed. Simulation and experimental results are provided to verify the validity of the proposed equalizer.