Current charging topology has the problem of a too wide switching frequency range. This paper proposes an IPOS dual LLC resonant converter suitable for battery charging, and conducts research on its constant voltage and constant current output characteristics. The proposed converter includes two sets of LLC resonant tanks. One set of resonant capacitor parameters is changed through the opening and closing of the auxiliary switch S, so as to realize the constant voltage and constant current output of the converter. In this mode, the converters all work at a fixed switching frequency: in the constant voltage mode (when S is closed), the two sets of resonant tanks work at the LC series resonance point; in the constant current mode (when S is off), one set of resonant tanks work at the LLC resonance point to achieve constant current output while the other group is still in the constant voltage mode. The proposed converter achieves soft switching while realizing the multiplexing of the primary side switches and the secondary side rectifier diodes. This paper introduces its working principle, voltage and current gain, design method and control scheme in detail. Finally, the feasibility of the proposed converter is verified through experiments and simulations. This work is supported by the National Natural Science Foundation of China (No. 61672337).