Sealing body and battery

In the present invention, a nickel-metal hydride secondary cell 2 is provided with a sealing body 11 for sealing an opening of an exterior case 10, wherein the sealing body 11 includes a sealing plate14 and a positive electrode cap 20 welded to the sealing plate 14, and the positive electrode cap 20 includes a cylindrical body section 40, an annular flange 42 disposed along the circumferential edge of an opening 45 located at the base end 41 of the body section 40, and a top wall 44 disposed so as to close a tip part 43 located on the side opposite from the base end 41. When the length from the center C of the flange 42 to the outer circumferential edge 64 of the flange is defined as R, and the length from a radial outer edge 66 of the flange at a weld part 60 to the outer circumferentialedge 64 of the flange is defined as X, the weld part 60 where the sealing plate 14 and the positive electrode cap 20 are welded together is located at a position where the proportion of X to R in percent is between 0% and 2%.