As the growing of portable electronic devises, lithium batteries play an important rule in power management systems. In order to maximize the performance of lithium batteries, a high charging efficiency and less charging time are required. Today, the main charging method for lithium batteries is the constant current- constant voltage method (CC-CV), but it can not reaches the requirement of fast charging. This thesis presents a fast charging method, which improve charging speed at the cost of minimum charging efficiency. First, we search the relationship between battery equivalent models and charging efficiency, then we control charging efficiency to have optimum charging current. Using the proposed algorithm, the charging time improve 12.4%, and the charging efficiency barely decreases 0.73%.