A battery cell comprising a battery housing case formed with a through hole communicating with an interior space, a hollow rivet, and a seal rubber. The hollow rivet has a seal surface annularly extending outside the battery housing case, and a hollow portion formed with an exhaust port continuous to the inner edge of the seal surface and positioned at the through hole to allow gas in the interior space to flow out through the exhaust port. The seal rubber has a contact unit extending annularly facing the seal surface to press the seal surface and is provided so as to close the exhaust port. The contact unit is formed to project toward the seal surface so as to contact the seal surface at a position away from the inner edge of the seal surface. Such an arrangement prevents an electrolyte leakage over a long period of time.