A method of manufacturing a flexible-film primary battery includes forming a first conductive carbon layer directly on a surface-treated inner surface of a first pouch film to form a positive electrode collector, and forming a positive electrode layer on the first conductive carbon layer to form a positive electrode plate. A second conductive carbon layer is formed directly on a surface-treated inner surface of a second pouch film to form a negative electrode collector, and a negative electrode layer is formed on the second conductive carbon layer to form a negative electrode plate. An adhesion/post-injection polymer electrolyte layer is inserted between the positive electrode plate and the negative electrode plate to manufacture a battery assembly. An electrolyte is injected into the polymer electrolyte layer of the battery assembly. The battery assembly is sealed completely to form a primary battery.