Currently, lithium battery packs are widely used in electric vehicles, portable electronic devices, and renewable energy systems. In response to issues such as overcharging and over-discharging that arise during the use of lithium battery packs, a study was conducted on bidirectional Buck-Boost converters. The working principles of these converters and the charge-discharge characteristics of lithium battery packs were analyzed. A dual closed-loop control scheme for voltage and current was implemented, leading to the design of a constant current and constant voltage charging control strategy. Key parameter designs for the lithium battery charge-discharge system were summarized, and a prototype was constructed. Constant voltage and constant current charge-discharge tests were performed, achieving 1% accuracy in voltage and current control. This validated both the correctness and effectiveness of the design. The improvements made enhance the performance and lifespan of lithium battery packs during usage, providing significant insights for practical engineering applications.