This thesis applies a zero-current-transition pulse-width-modulated boost converter in a battery charger. The battery charger with zero-current-transition pulse-width-modulated technology can significantly reduce the switching losses, constant-frequency control and maintain the voltage/current stress on the circuit components when the power transistor is switched under zero-current condition. The equivalent circuits of various modes are constructed based on analyzing the operating principles of the circuit according to the turn-on conditions of the switches.Experimental results have demonstrated the theoretical effectiveness of the presented battery charger circuit. The practical mean charging efficiency of the proposed battery charger is 92.87%.