(a) a battery element having a cathode, an anode, a polymer electrolyte, and terminals extending from the cathode and the anode;

(b) a package body having (i) a first area with a housing recessed part in which the battery element is housed, (ii) a second area contiguous to and extending from the first area, the second area and the first area separated by a first folding edge, the first folding edge located in a side opposite to that of the terminals relative to the first area, the second area overlying an exposed upper surface of the battery element, and (iii) a third area contiguous to and extending from the second area so as to extend in a direction substantially perpendicular to the first area, the third area and the second area separated by a second folding edge;

(c) a frame disposed along a periphery of the housing recessed part, the frame comprising (i) a front wall part disposed in the terminal side of the battery element, (ii) a rear wall part disposed in a side opposite to the terminals of the battery element and (iii) side wall parts disposed in the side surface parts of the battery element, the frame surrounding the first, second and third areas along a thickness direction of the battery element; and

(d) a connecting board disposed in the frame to which the terminals are connected and having a terminal part electrically connected to an external device,

wherein,

the packaged body is folded along the first folding edge so that the second area is in contact with the first area along a periphery of the battery element,

the terminals of the battery element are connected to the connecting board, and

the packaged body is folded along the second folding edge so that the third area overlies and is in contact with an exposed surface of the first area.