A system for charging and discharging batteries includes a battery module, an adapter, a charger, and an electronic device electrically connected to the charger and the battery module. The battery module includes a first cell battery, a second cell battery, and a first switch electrically connected to the first and second battery cells. The adapter receives an AC voltage, and converts the AC voltage to a DC voltage. The charger receives the DC voltage, and charges the battery module accordingly. The electronic device is electrically connected to the charger and the battery module. When the charger charges the battery module, the first switch is switched to electrically connect the first and second battery cells with the charger in series. When the battery module discharges to the electronic device, the first switch is switched to electrically connect the first and second battery cells with the electronic device in parallel.