A sealed battery has a generator element enclosed within an external casing. An opening in the external casing is covered by a closure cap in which an injection hole for injecting electrolyte is provided. The injection hole is sealed using a sealing plug which is composed of a support member that is fixed on a surface of the closure cap so as to cover the injection hole and a plugging member that is at least partially formed of an elastic material and is supported by the support member so as to plug the injection hole. The plugging member is formed of an elastic material and is pressed into the injection hole by the support member. As a result, an airtight seal can be easily and securely achieved for the injection hole. The support member can be made large to facilitate handling, thereby reducing the likelihood of the sealing plug being improperly supplied during attachment to the injection hole.