An electrochemical cell having an open ended cylindrical housing and an end cap assembly inserted therein closing said housing, said end cap assembly comprising an end cap functioning as a cell terminal and an insulating sealing member electrically insulating the end cap from the cell housing, said insulating sealing member having an elongated electrically conductive current collector passing therethrough, the current collector being in electrical contact with the end cap, and the edge of said housing being crimped over the peripheral edge of said end cap to form a cell shoulder along the line of crimp, the improvement comprising: the end cap assembly comprising an end cap, and an insulating sealing member underlying said end cap when the cell is viewed in vertical position with the end cap assembly on top; said end cap being formed of a disk of single piece metallic construction having a convoluted surface and at least one vent aperture through its surface; wherein said end cap assembly does not include a metal disk other than said end cap within any portion of said cell housing at the open end thereof; said insulating member comprising an insulating sealing disk abutting the cell housing and electrically insulating said end cap from the cell housing; said insulating sealing disk having a central boss and an integrally formed radially extending arm extending from said boss; wherein said radially extending arm forms a continuous surface; said radially extending arm having a thinned portion therein forming a rupturable membrane which underlies said end cap when the cell is viewed in vertical position with the end cap assembly on top; wherein when gas pressure within the cell reaches a pressure in a range between about 150 and 900 psig (1034 x 10 3 and 6206 x 10 3 pascal gage), said membrane ruptures thereby releasing gas directly into the surrounding environment through said vent aperture in the end cap; wherein said thinned portion forming said membrane is formed by the base of a groove cut into at least one of the top and bottom surfaces of said radially extending arm, when the cell is viewed in vertical orientation with the end cap assembly on top, wherein said groove is an annular V-shaped groove circumventing the cell's longitudinal axis and wherein the width of the cut groove at the groove base is between 0.1 to 1.0 mm. the end cap assembly comprising an end cap, and an insulating sealing member underlying said end cap when the cell is viewed in vertical position with the end cap assembly on top; said end cap being formed of a disk of single piece metallic construction having a convoluted surface and at least one vent aperture through its surface; wherein said end cap assembly does not include a metal disk other than said end cap within any portion of said cell housing at the open end thereof; said insulating member comprising an insulating sealing disk abutting the cell housing and electrically insulating said end cap from the cell housing; said insulating sealing disk having a central boss and an integrally formed radially extending arm extending from said boss; wherein said radially extending arm forms a continuous surface; said radially extending arm having a thinned portion therein forming a rupturable membrane which underlies said end cap when the cell is viewed in vertical position with the end cap assembly on top; wherein when gas pressure within the cell reaches a pressure in a range between about 150 and 900 psig (1034 x 10 3 and 6206 x 10 3 pascal gage), said membrane ruptures thereby releasing gas directly into the surrounding environment through said vent aperture in the end cap; wherein said thinned portion forming said membrane is formed by the base of a groove cut into at least one of the top and bottom surfaces of said radially extending arm, when the cell is viewed in vertical orientation with the end cap assembly on top, wherein said groove is an annular V-shaped groove circumventing the cell's longitudinal axis and wherein the width of the cut groove at the groove base is between 0.1 to 1.0 mm.