Abstract: Energy storage batteries are currently composed of a large number of low-voltage battery cells. The states of charge of the cells are different due to the characteristic diacrepancy between the cells, which causes some cells to be overcharged. A charger with voltage equalization function based on an immittance network is proposed in this paper. This charger can implements the two-stage charging mode of constant current and constant voltage with only a single voltage loop. The principle of the equalizer is analyzed. The influence of the voltage difference between the cells on the initial working voltage of the equalizer is presented and the equivalent circuit of the proposed complete topology is also given. The experimental results show that the proposed charger simultaneously achieves the high efficiency and the requirement of voltage equalization between the cells.