A manufacturing method for a flexible battery including injecting an electrolyte into an opening of an exterior material accommodating an electrode assembly contained therein and impregnating the electrode assembly with the electrolyte through a pressure difference inside the exterior material; and a sealing step of sealing the opening. Because the electrode assembly provided in the battery can be completely impregnated with an electrolyte, no spot occurs on the surface of a negative electrode filled with the electrolyte. In addition, the flexible battery can prevent or minimize deterioration of physical characteristics that the battery is required to exhibit, even if repeated bending occurs.