During the whole charging process, the charging current is kept constant by adjusting the output voltage. Keeping the charging current constant, the charging rate is relatively low. The control method of constant current charging is simple, but because the acceptable current capacity of lithium-ion battery pack decreases gradually with the charging process, the power lithium battery's receiving capacity decreases at the late charging stage, and the charging current utilization rate decreases greatly. The advantages of this method are simple operation, convenient, easy to implement, easy to calculate the charging amount.