This invention proposes a novel charging method for improving the efficiency of charging a super capacitor. The method comprises the steps of: charging the super capacitor with a first current; measuring a voltage of the super capacitor; stopping the supply of the first current when the measured voltage reaches a pre-defined voltage value; monitoring a voltage variation of the super capacitor; charging the super capacitor with a second current when the monitored voltage variation exceeds a pre-defined threshold within a pre-defined period. By using said two-phase charging, especially when using two different charging currents, it is easier to improve the charging efficiency without degrading the charging speed.