Abstract: A method of charging a battery includes following steps: First, a charging voltage is provided to charge the battery. Afterward, a charging control variable is judged whether to reach to an adjustment value. Afterward, the charging voltage is adjusted with a first voltage difference to continuously charge the battery when the charging control variable reaches to the adjustment value. Afterward, a health state value of the battery is judged whether less than or equal to a critical health state value. Finally, the charging voltage is increased with a second voltage difference to continuously charge the battery when the health state value of the battery is less than or equal to the critical health state value.