PURPOSE: To absorb and reduce heat energy close to a weld zone and to stably obtain welding strength by cooling a battery and then, welding a lead wire or lead terminals to battery terminal parts.

CONSTITUTION: After the battery is cooled, the lead wire or the lead terminals 7 and 8 are welded to the battery terminal parts. Consequently, even if welding power is increased, the influence is not exerted upon battery characteristics and the range which can be welded is extended. Accordingly, when welding conditions are slightly changed or even when material, thickness, plating, shapes, etc., of the battery terminals or the lead terminals or the lead wire are changed, the welding conditions can be easily set.