This work proposes a novel battery charger circuit with an improved parallel-loaded resonant converter use in rechargeable batteries in mobile power applications. The proposed topology is composed of an improved parallel-loaded resonant inverter and a bridge rectifier. The output voltage of the improved parallel-loaded resonant converter is filtered by an electrolytic capacitor. This topology has advantages over the traditional parallel-loaded resonant converter of smaller size, lower weight and lower cost. The operating principles of the proposed charger circuit are thoroughly analyzed. A prototype charger circuit with the improved parallel-loaded resonant converter implemented for a 12V 12000mAh rechargeable battery of mobile power is constructed and tested to verify the theoretical predictions. The measured energy conversion efficiency of the improved parallel-loaded resonant topology reaches up to 91.2%. The test results demonstrate that the novel topology provides a satisfactory performance. The improved parallel-loaded resonant converter has great potential for use in power-related devices in electronic products, such as standby power supplies for laptop computers, communication equipment, consumer electronics, and telecom power supplies.