Batteries are extensively adopted in various applications, such as telecommunication power supply, electric vehicles, uninterruptible power supplies, photovoltaic systems and portable electronics products. The charge mode significantly influences the battery life and capacity. To provide a normal electricity supply to a load, charging methods replenish the energy to a battery to continue a normal power supply. The conventionally adopted battery charger with a large volume engendering power dissipation during charging is well-known to have low efficiency. The charging technique is critical for increasing the charging efficiency and extending the battery life. The traditional battery charger with a buck converter has a simple structure and high efficiency in low-frequency switching, but suffers large switching losses in high-frequency switching. The buck ZCS converter is used to resolve the high-frequency switching losses, and also to reduce the circuit volume.