A battery device that functions as a power source of a tool main body and is attachable to a body of a user may include a battery housing that is capable of removably receiving at least one rechargeable battery and capable of being electrically connected to the at least one battery, an adaptor that is capable of being electrically connected to the tool main body, and a cable electrically connecting the battery housing and the adaptor. The battery housing comprises a housing body that is constructed to be attached to the body of the user and is capable of receiving the at least one battery therein, and a cover member that is openably and closably attached to the housing body. The housing body and the at least one battery are connected to each other via a male-female engagement device. The male-female engagement device has an engagement release portion that is positioned so as to be exposed when the cover member is opened relative to the housing body.