A card type device serving as a supplementary power supply device, and a host using the same. The card type device may include a battery provided in a frame to serve as a supplementary power supply to the host, a connector to connect to the host for an interfacing of power and data to and/or from the host, a battery charging/discharging circuit to charge the battery with an input power supplied via the connector, and to output the power of the battery via the connector. A power input/output controller provides the host with information of attributes of the battery during a connection to the host, with the power input/output controller to control the battery charging/discharging circuit so that the power of the battery is supplied to the host when a request for power supply is transmitted from the host. The power input/output controller controls the battery charging/discharging circuit so that the battery is charged with the input power when the battery is completely discharged. Further, the battery charging/discharging circuit is a smart battery circuit, and the smart battery circuit provides the host with information of attributes of the battery via an address pin of the connector. The information of the attributes of the battery, provided to the host, include at least one of a battery voltage, a battery remnant, battery charging times, a battery manufacturer, and a battery manufacturing period.