The invention provides a battery including a power generating element container, a positive electrode mixture, and a hydrogen gas permeable sheet provided in an opening of the power generating element container, the hydrogen gas permeable sheet having a water repellence of 2 kPa or more and a He gas permeability at 30.degree. C. in a range of 2.times.10.sup.-6 to 10000.times.10.sup.-6 (cm.sup.3 (STP) cm/seccm.sup.2cmHg), wherein a distance between the positive electrode mixture and the hydrogen gas permeable sheet gradually decreases toward a side wall of the power generating element container.