Battery pack

1. A battery pack comprising:

an external case; and

a thin outline battery held in the external case, the battery having a thickness that is smaller than its width;

wherein the external case is provided with openings which expose a front surface and a back surface of the thin outline battery to the outside, the external case is formed in the shape of a rectangular frame which covers both sides and both ends of the thin outline, and the thickness of the external case is substantially equal to the thickness of the thin outline battery or the external case is thinner than the thin outline battery,

wherein the external case comprises a first case section and a second case section divided between the front and back surfaces of the thin outline battery, each of the first case section and the second case section comprising side wall case sections and end region case sections, respectively, such that the first case section and the second case section hold the thin outline battery by connecting side wall case sections and end region case sections, respectively, and

wherein the thin outline battery has first curved surfaces at both side walls, the first curved surfaces of the side walls defining rounded corner edges and central protruding regions, the side wall case sections have second curved surfaces which at least partially complement the first curved surfaces, the edges of the side wall case sections being positioned at the rounded corner edges of the thin outline battery to mate the edges of the side wall case sections with the rounded corner edges of the thin outline battery by contacting the first curved surfaces of the side walls with the second curved surfaces of the side wall case sections such that the external case holds both sides of the thin outline battery with the side wall case sections thereby preventing the thin outline battery from falling out in the front or back directions of the thin outline battery.

2. A battery pack as recited in claim 1 , wherein the side wall case sections cover both sides of the thin outline battery and the end region case sections cover both ends of the thin outline battery, and wherein inside surfaces of the side wall case sections are provided with retaining troughs and central protruding regions on both sides of the thin outline battery are inserted into these retaining troughs.

3. A battery pack as recited in claim 1 , wherein the thin outline battery is adhesively bonded and fixed to inside surfaces of the external case.

4. A battery pack as recited in claim 3 , wherein adhesive bond application cavities are provided on the inside surfaces of the external case in regions opposite the thin outline battery, and an adhesive bond supplied into the adhesive bond application cavities adheres the thin outline battery to the external case.

5. A battery pack as recited in claim 4 , wherein the external case forms a handling clasp integrally protruding from an area located outside of a region provided with one of the adhesive bond application cavities.

6. A battery pack as recited in claim 1 wherein a terminal holder for output terminals is disposed in one of the end region case sections or one of the side wall case sections of the external case.

7. A battery pack as recited in claim 1 , wherein the first case section and the second case section are joined by weld attachment.

8. A battery pack as recited in claim 1 , wherein the thin outline battery and the external case are covered by an insulating sheet.

9. A battery pack as recited in claim 1 , wherein one part of a peripheral edge of an insulating sheet is attached such that it straddles both the front and back surfaces of the external case.

10. A battery pack as recited in claim 8 , wherein attachment surfaces of the thin outline battery and the external case to which the insulating sheet is attached have non-planar regions; and the insulating sheet is formed to fit along these non-planar regions and is attached to attachment surfaces of the thin outline battery and the external case.

11. A battery pack as recited in claim 10 , wherein the insulating sheet is surface treated to keep non-planar shapes formed along the non-planar regions from standing out.

12. A battery pack as recited in claim 1 , wherein surfaces of the thin outline battery are covered by an insulating sheet, edge regions of the insulating sheet are disposed between the thin outline battery and the external case, and the insulating sheet edge regions are sandwiched between the thin outline battery and the external case.

13. A battery pack as recited in claim 12 , wherein the thin outline battery has a cap region, and the insulating sheet is disposed over the thin outline battery cap region, and the thin outline battery cap region is insulated by the insulating sheet.

14. A battery pack as recited in claim 12 , wherein all perimeter edges of the insulating sheet are inserted, and sandwiched between the thin outline battery and the external case.

15. A battery pack as recited in claim 12 , wherein the insulating sheet includes two pieces of insulating sheet, and the front and back surfaces of the thin outline battery are covered by the two pieces of insulating sheet.

16. A battery pack as recited in claim 12 , wherein the insulating sheet comprises a single piece of insulating sheet, and the front and back surfaces of the thin outline battery are covered by the single piece of insulating sheet which is wrapped around the thin outline battery in a U-shape.

17. A battery pack as recited in claim 1 , wherein a compartment to hold protection circuitry is provided in one of the end region case sections or one of the side wall case sections which houses the output terminals, and protection circuitry is installed in the compartment and insulated from the outside.

18. A battery pack as recited in claim 1 , wherein a terminal holder, which disposes output terminals in fixed positions, contains protection circuitry, and the terminal holder is housed in one of the end region case sections or one of the side wall case sections of the external case.

19. A battery pack as recited in claim 1 , wherein an insulating ring is disposed at an end plane of the thin outline battery that is provided with a protruding electrode, the insulating ring has a through hole, and the protruding electrode is inserted into the through hole to insulate the battery end plane.