A battery-cell structure of a battery is constructed to have a resinous spacer 5 with a frame shape surrounding thick central portions between a battery cell 3 arranged at an upper side and a battery cell 4 arranged at a lower side, and ventilation portions 62 and 64 that are provided in the resinous lower case 6 to communicate the exterior with depressed portions 61 of the resinous lower case 6 and have an up- and down symmetrical shape and size. It is constructed so that the battery cell 3 arranged at the upper side and the battery cell 4 arranged at the lower side are put in a vertical direction between the resinous lower case 6, the spacer 5 and the upper case 2.