this battery pack is assembled by welding an opening portion of a waterproof bag to provide an insertion opening that is smaller than the total opening width but allows a battery core pack to be inserted , inserting the battery core pack into the waterproof bag , then , closing the opening portion of the waterproof bag , and placing the waterproof bag , in which the battery core pack has been placed , into an external case . in this way , this battery pack can be assembled efficiently , with the battery core pack having been given a waterproof structure by the waterproof bag while in an ideal state .