A portable terminal includes a charging control system. The system supplies electric power to the battery. If the battery is charged completely, the system stops charging the battery temporarily, adjusts the termination current, and then charges the battery to the preset second charge capacity. The system can recharge the battery if the battery of the second charge capacity under goes a natural discharge for a certain time period by a certain rate of the second charge capacity, for example, 1%, or if the maximum voltage corresponding to the second charge capacity drops by 1% of the maximum voltage. Therefore, the system can retail the maximum charged state of the battery.