Hermetically sealed battery

A hermetically sealed battery is provided, equipped with a opening sealing unit 10 including a Positive Temperature Coefficient (PTC) element without reducing the volume of the outside can, and capable of preventing the generation of a large current in case a short circuit occurs as well as enhancing operational security. The opening sealing unit 10 according to the invention comprises a bottom plate 11 for closing the opening of the outside can 18 , a positive electrode cap 12 forming a space for storing a pressure valve, said positive electrode cap being used as a terminal for the positive electrode, a resilient valve 14 having a steel plate 14 a on the upper surface, a spring 15 and a PTC element ring 16 disposed on the flange 12 a in the positive electrode cap 12 . An insulation gasket 17 is mounted onto the periphery of the opening sealing unit 10 to hermetically close the opening of the outside can 18.