PURPOSE: To lessen the degrading of battery capacity during aging as well as the period of no use after shipment by piercing an air hole whose diameter is small as compared with the thickness of the bottom plane of a battery case by using a laser beam.
CONSTITUTION: A circular recessed part 9 is formed in the bottom plane of a case 1 and a battery is prepared by using the case and after aging, laser beam is radiated to the recessed part 9 of the case of the battery from the outside of the case to form an air hole. In this case, the diameter of the hole 9 is made smaller than the thickness of the bottom plane of the case 1 of the battery. Consequently, after assembly of the battery, capacity degrading during aging becomes almost zero since an air hole is not formed in aging process and the process for making a hole in the case pressing process is abolished, so that the life time of a pressing die is extended and pressing speed is increased.
MIZUTANI SEIICHI
TSURUYA SHINJI
MORITA KORENOBU
