Abstract: A system is developed to improve the series battery packs concerning their uniformity and charging protection. Measures for the implementation of battery equalization during charging and the protection system are discussed. Functions of equalization charging and overcharging protection are analyzed, and model of control for series battery packs equalization charging is setup. Diverting-current and feedback bus voltage are measured during experiments on series Li-ion battery packs equalization charging. Field operation on luxury transit bus BFC6100EV showed that the system did improve on the battery series charging uniformity provided overcharging protection, enhanced battery performance and prolonged battery life.