A 3.5 kW digital controlled battery charger is implemented with the ripple feed forward (RFF) technique to reduce the output voltage ripple. This battery charger is composed of front-stage of interleaved boost converter for PFC and full-bridge resonant converter for DC-DC conversion. The full load conversion efficiency of the full-bridge resonant converter is 94.3%, and the highest efficiency of system is 93.9%. Mostly, the output voltage ripple is reduced about 30 % by using the RFF.