Due to the differences in batteries of a series-connected battery bank, the restored capacity in each battery may not be the same when being charged. In order to extend battery cycle life, the charger for the battery bank must have the capability of charging equalization. This thesis proposes a non-dissipative balance charging circuit based on buck-boost topology for a series-connected battery bank. Each battery in a battery bank is associated with a buck-boost converter. This topology can efficiently alleviate the unbalance of charge among batteries by taking off the charge from the affluently charged batteries and then allotting to those insufficient ones. To accomplish this complicated and accurate control, a digital signal processor (DSP) with sensors and interface circuits is adopted. It monitors the variations of battery voltages, activates the associated buck-boost converter, and adjusts the duty ratio of the converter to regulate the energy to be released. In virtue of the adoption of digital control kernel, the control circuit can be simple and the control flexibility can be favored. A battery bank with four series connected lead-acid batteries is used for illustrating the operating behavior and describing the operation modes of the balance charging circuit. The results of experiments convincingly advocate the applicability of the proposed approach.