An isolated balance charger for series-connected batteries is proposed in this paper. With the proposed charger, the balanced charging power is directly provided to the series-connected batteries without any additional energy moving process between the batteries. The proposed charger is composed of an isolated dual half-bridge dc converter and two dual output converters. Operational principles and control strategy are illustrated in this paper. A low-cost microcontroller unit is adopted to implement the digital controller with fed-back voltage and current signals of the batteries. A prototype for four 12V 22Ah series-connected batteries is constructed. From the experimental results, the performance and validity of the proposed charger can then be verified. Compared with the conventional charger, the charging efficiency can be improved by 8.3%.