Heretofore, a rechargeable secondary battery such as a lithium ion battery has been available for e.g. power supply to an in-vehicle equipment of a vehicle, a power source of a battery mounting device, etc. The secondary battery generally includes a power generating element constituted of a wound electrode body made by winding positive and negative electrode sheets and separator sheets in laminated relation and impregnating them with electrolyte. The secondary battery is normally configured such that the wound electrode body is hermetically sealed in a case. As a winding manner of the wound electrode body, there are flat winding, cylindrical winding, and others. The shape of the case depends on the winding manner. A case for a flat wound electrode body has a flat shape.
In some cases, plural secondary batteries are assembled to provide a battery assembly in order to comply with the details of electric power required by a power supply destination. In the case of assembling the flat-type secondary batteries into a battery assembly, the secondary batteries are arranged in a direction of thickness of each battery and entirely bound into one unit by an appropriate binding member. In this bound state, each of the secondary batteries is pressed in the thickness direction. It has been known that appropriate application of the pressing load on the wound electrode bodies is important in power generation capability of the secondary batteries. An example of such secondary battery is disclosed in for example Patent Literature 1.