A sealing member that exhibits both the effect of suppressing permeation and leakage of an electrolytic solution and the effect of decreasing the incidence of damage to the sealing member is provided. A sealing member for a battery includes a non-aqueous electrolytic solution, where a material constituting the sealing member contains an elastic material. A compression rate R of the sealing member when attached is 50% or more. The sealing member satisfies Eb≥a×βb, where Eb is an elongation at break of the material constituting the sealing member as measured in accordance with JIS K 6251, β is a cross-sectional aspect ratio, a=6.919×R−2.066, and b=2.278×R−1.767.