Abstract: A battery holder comprises first and second caps and a cylindrical socket. The socket forms two spaces therein separated by an abutment midway of the socket and each opening at one end of the socket. Each space holds a battery with the central pole contact thereof positioned at the end of the socket. The socket is positioned selectively with one battery or the other engaging the contacts located at the first cap. Clamping means holds the caps together with the socket there between. The socket forms an outside circumferential groove at each end thereof and in each groove forms at least one slot through the cylindrical wall of the socket, extending over a minor part of the circumferential length of the groove. An elastic O-ring is received in each groove forming a straight portion extending through the slot inside the socket.