This technology relates to a battery device, a control method, and an electric vehicle capable of providing a highly secure anti-theft function. A battery outputs DC power through a power line, a reader/writer communicates by outputting a high-frequency signal through the power line to read authentication information of an electronic device when the electronic device is connected to the battery through the power line, a microcomputer stores the read authentication information and controls the battery when first connection to the electronic device is performed, and performs an authentication process of the electronic device based on the read authentication information and the authentication information stored in the first connection and controls the battery according to a result of the authentication process of the electronic device when second or subsequent connection to the electronic device is performed. This technology may be applied to the battery device mounted on a power-assisted bicycle, for example.