Abstract: Lithium-ion batteries are commonly used as loads in current wireless power supply applications. The wireless battery charger should provide an initial constant current（CC） and a subsequent constant voltage（CV） output required by the battery. The additional converter at the secondary side, the hybrid topology, or the high-order network can realize CC-to-CV transition, which have the problems of complicated control and poor reliability. To solve this problem, this paper proposes a three-coil wireless battery charging system with self-adaptation to the battery charging curve. By adding an auxiliary coil and a passive rectifier bridge at the primary side, the system can automatically realize CC-to-CV transition without any additional control. The auxiliary coil is connected in parallel with the input source through a specific compensation network, and the output voltage threshold is not limited by the magnetic coupling mechanism parameter. Thus the self-adaptation to the battery charging curve is realized. Meanwhile, the proposed three-coil wireless battery charger operates at the same frequency in both charging modes, which ensures the soft switching of the inverter and the near-zero reactive power circulation of the converter, to reduce the device stress and improve the transmission efficiency. Moreover, the proposed charger has the function of automatic open-circuit protection. In this paper, the design principles and operation principle of the charger are systematically described, and an experimental prototype with 72 V/2.5 A output is built to verify the effectiveness of the proposed charger.