PURPOSE: To prevent the movement of batteries within a jacket and to absorb shock from the outside by arranging an insulating elastic support inside a jacket having built-in batteries and a PTC device which increases electric resistance with an increase in temperature.

CONSTITUTION: An insulating elastic support 8 is arranged on each of the bottom and the inside of a cover of a jacket 12 having built-in high output batteries 10 and a PTC device 1. The elastic support 8 is also arranged on the inside surface of the jacket 10 to fix the batteries. An empty part can be formed in the bottom or the upper part of the jacket 12, and the elastic support can be arranged on the whole inner surface of the jacket 12. High power primary lithium batteries are used as battereis 10. The material of the ealstic support 8 is selected from a group of natural rubber, isoprene rubber, butadiane rubber, styrene-butadiane rubber, chloroprene rubber, various silicone rubber and fluorine rubber.