To provide a technology for improving productivity in a sealing process by avoiding a sealing failure occurring when sealing a liquid intake port provided on a battery seal, and secure long-term reliability in preventing liquid leakage after fitting.

A sealing plug 21 includes a lid 22 of a flat shape and a plug 23 provided so as to project in a central part of the lid, and includes an annular elastic member 24 between the intake port 20 and the sealing plug 21 arranged so as to cover the intake port. The lid 22 is arranged so as to cover the electrolyte solution intake port of the battery seal 10, and the plug 23 is inserted into the intake port opened on the battery seal through an inner air gap of the annular elastic member 24. By pressure contacting the annular elastic member 24 with the sealing plug formed of a sidewall of the intake port, the lid, and the plug, welding between the sealing plug 21 and the battery seal 10 is sufficiently carried out to securely seal. Therefore, the sealed battery with high reliability can be provided.