Patent ID: 7678492

Claim:
A lead acid battery cover adapted to seal an automotive vehicle battery casing having a design pressure maximum, the lead acid battery cover comprising: a rigid, porous frit consisting of modified polytetrafluoroethylene, wherein the frit allows gases to escape while preventing liquid from escaping and acts as a blowout disk when a pressure within said automotive vehicle battery casing exceeds a predetermined pressure that blows said frit out of said lead acid battery cover, wherein the predetermined pressure is within 5% to 10% of the design pressure maximum of the automotive vehicle battery casing; and restraining means for holding said frit in said lead acid battery cover until said predetermined pressure is exceeded, wherein the modified polvtetrafluoroethylene comprises Polytetrafluoroethylene, from 1 wt % to 35 wt % PMMA and from 1 wt % to 7 wt % lubricant.