RECHARGEABLE BATTERY AND BATTERY SYSTEM

A secondary battery 101 in accordance with the present invention includes a secondary battery 101 including a square battery can 1 including a positive electrode terminal 8 and a negative electrode terminal 9, an electrode assembly G disposed in the square battery can 1, and formed of a sheet-shaped positive electrode 2 electrically connected to the positive electrode terminal 8 and a sheet-shaped negative electrode 3 electrically connected to the negative electrode terminal 9 to be laminated with a separator interposed therebetween, and first and second auxiliary insulating sheets 4 which are respectively disposed at opposite positions on long sides of a surface of the square battery can 1 on which the positive electrode terminal 8 and the negative electrode terminal 9 are formed to sandwich the electrode assembly G. The secondary battery is characterized by first and second retainers 5 having substantially the same width as an internal length of the square battery can 1 in a direction of the short side of the surface, and disposed at opposite positions on the short sides so as to sandwich the electrode assembly G, the first and second retainers 5 being in contact with the square battery can 1 at a plurality of points to support the electrode assembly G.