A battery includes a first power generating element including a first electrode layer and a first counter electrode layer, a first current collector that is in contact with the first electrode layer, a second current collector that is in contact with the first counter electrode layer, a first sealing portion that seals a gap between the first current collector and the second current collector, a first void disposed between the first sealing portion and the first power generating element, and a first gas detection unit that detects gas. The first gas detection unit detects “the gas in the first void”.