A charging apparatus includes a power conversion circuit for charging a battery, and a charging control circuit. The battery has a battery net voltage. The charging control circuit includes a conversion control circuit, a sensing circuit and a determining circuit. The conversion control circuit controls the power conversion circuit to generate plural pairs of DC output voltage levels and DC output current levels, wherein each DC output voltage level and its corresponding DC output current level are a voltage-current pair. The sensing circuit senses the DC output voltage levels and/or the DC output current levels. The determining circuit determines the battery net voltage according to plural voltage-current pairs.