To reduce circuit complexity and better control the charging current for parallel charging, a switching-based charger with an adaptive hybrid duty cycle control (AHDCC) for multiple batteries is presented. Depending on the voltage difference of the batteries, the AHDCC mechanism automatically delivers a different amount of energy to each battery to realize battery voltage balance and reduce power losses. Since an intermittent charging method is adopted in the constant current (CC) mode, the effect of voltage drop across the battery's parasitic resistor can be removed, and thus the charging time in CC mode is prolonged. AHDCC adjusts the charging current, prolongs the charging period in CC mode, and entirely turns on the auxiliary switches in the constant voltage mode. As a result, the functionalities of fast charging and battery voltage balance can be realized concurrently. The experimental results demonstrate that the peak efficiency of the charger is up to 89.4% and the total charging time of two batteries is slightly smaller than that of a single battery.