Due to the price of crude oil is continuously increased, the price of raw material in the national economy and the people’s livelihood is rised. Traffic rate, charges for water and electricity, gas price and so on are also going up. Solar energy, one of renewable energies, is become the best plan for treating the continuous increasing price of crude oil. This thesis realizes a solar energy battery charger with series-parallel resonant converter. The circuit parameters are designed from the derived circuit equations. Experimental results have demonstrated the theoretical effectiveness of the proposed battery charger circuit. The practical mean charging efficiency of the developed battery charger is 89.6%.