A battery module for a portable electronic device is disclosed. The battery module is connected with the portable electronic device with at least three contacts. The battery module includes a battery, a recognition circuit, and a thermal sensing circuit. The recognition circuit has an energy storage element and a current limiting element, and the thermal sensing circuit has a switch and a thermal sensing element. The thermal sensing element varies its electric parameter in accordance with the temperature of the battery module. With the charging curve of charging the energy storage element by way of the current limiting element, the portable electronic device can determine a battery type, and the thermal sensing circuit is then initiated to acquire the thermal information of the battery module.