Rechargeable battery

1. A rechargeable battery comprising:

an electrode assembly;

a case accommodating the electrode assembly;

a cap plate covering the case and having a first surface facing the electrode assembly and a second surface opposite the first surface, the cap plate including an injection hole extending from the first surface to the second surface and being sealed by a ball, the second surface having a recess depressed toward the first surface, the injection hole being arranged in the recess; and

a terminal plate covering the injection hole and the ball, the terminal plate including a first region in the recess below the second surface of the cap plate.

2. The rechargeable battery of claim 1 , wherein the terminal plate is welded to a region of the cap plate outside the injection hole.

3. The rechargeable battery of claim 1 , wherein the cap plate includes a first surface that is planar and faces the electrode assembly, a second surface that is planar, is located opposite to the first surface, and faces the terminal plate, a first protrusion part protruding from the first surface towards the electrode assembly, and a second protrusion part protruding from the second surface towards the terminal plate.

4. The rechargeable battery of claim 3 , wherein the injection hole includes a throughhole centrally formed in the first protrusion part.

5. The rechargeable battery of claim 4 , wherein the ball is coupled to the throughhole.

6. The rechargeable battery of claim 4 , wherein the first region of the terminal plate is planar and contacts a bottom surface of the recess, and

wherein the terminal plate further includes a slanted second region extending from the first region and contacting side surfaces of the recess, a planar third region extending from the second region and contacting the second surface of the cap plate, a slanted fourth region extending away from the third region and the second surface of the cap plate, a planar fifth region extending from the fourth region and welded to a bus bar, a planar sixth region extending from the fifth region and towards the second surface of the cap plate, and a planar seventh region extending from the sixth region and contacting the second surface of the cap plate.

7. The rechargeable battery of claim 6 , wherein a groove is formed in the seventh region of the terminal plate and wherein the second protrusion part of the cap plate is coupled to the groove.

8. The rechargeable battery of claim 6 , wherein the seventh region of the terminal plate is welded to the second protrusion part.

9. The rechargeable battery of claim 6 , wherein the third region of the terminal plate is welded to one region of the second surface of the cap plate.

10. The rechargeable battery of claim 6 , wherein a space is defined by the fourth, fifth, and sixth regions of the terminal plate.

11. The rechargeable battery of claim 1 , wherein the ball comprises a metal core and a resin coated on a surface of the metal core.