A thin rechargeable lithium battery having a battery main body enclosed between sealing members (a) and (b), at least sealing member (a) having a concave portion that extends to either side from a central position so as to have a peripheral collar portion (a-i) which surrounds the concave portion, sealing member (b) having a peripheral collar portion (b-i) corresponding to the collar portion (a-i) of sealing member (a) and the two sealing members (a) and (b) being opposingly arranged such that the face of said concave portion of sealing member (a) faces sealing member (b) through the battery main body, wherein collar portions (a-i) and (b-i) are mutually welded, and either sealing member (a) or (b) is provided with a power output terminal having electrical continuity with the battery main body and an insulating portion for insulating said terminal.