This article discusses the high efficiency battery charger's electrical specification, to find the good effect approach, and the actual manufacture battery charger. It proves that the experimental result and the principle correspond mutually. In battery charger's electricity circuit, the output inductor and capacitor is very important factor, and also more effective to battery charger's characteristic. So how to choose the suitable inductor, the capacitor, and the suitable work frequency, to design more efficiency battery charger electricity circuit is our goal.