SECONDARY BATTERY

A secondary battery includes a battery device, a container, and a cover part. The container contains the battery device. The cover part includes a cover member and a valve member. The cover member includes a first flange. The valve member includes a second flange, and is positioned between the cover member and the battery device in a first direction. The first flange includes a lower surface, an upper surface, and an end surface. The second flange is folded back to continuously cover the first flange from the lower surface, via the end surface, to the upper surface. An upper surface covering part of the second flange includes a first part having a first thickness and a second part having a second thickness smaller than the first thickness. The second part is positioned between the first part and the end surface in a radial direction of the container.