Battery vent plug

A battery vent plug for insertion into at least one battery vent well to vent and otherwise seal said well, comprising:

• a hollow upper cylindrical member having a top surface with at least one vent aperture defined therein;
• a hollow lower cylindrical member having an upper surface defining at least one aperture in said upper surface, at least a portion of said lower cylindrical member being fitted within and matingly engaging the interior surface of said upper cylindrical member;
• a gas permeable diaphragm sealingly engaging said upper surface of said lower cylindrical member at least around said aperture defined therein, said diaphragm being retained between generally opposing surfaces of said cylindrical members;
• an o-ring gasket positioned around the outer cylindrical surface of said lower cylindrical member for engaging the interior walls of the battery case vent well to provide a gas-tight seal against said battery case vent well when said plug is disposed therein, said o-ring gasket having a greater diameter than that of said vent well so that upon insertion of said plug into said vent well said o-ring is compressed between said vent well and the remainder of said plug;
• and a retaining means for retaining said gasket with respect to said plug comprising an annular ridge formed on the exterior surface of said lower cylindrical member, said ridge cooperating with the lower end of said upper cylindrical member to retain said o-ring gasket therebetween.