NOVELTY - The microporous silica-filled polyethylene separator comprises cured rubber powder particles. The particles: have a low particle porosity (10%) and an antimony selectivity factor of greater than 1.10 as determined by the Antimony Suppression Test; contain an active ingredient, carbon black colorant and silica; and exhibit a low rate of diffusion of the active ingredient out of the particles and out of the separator through a controlled release mechanism and property of increasing hydrogen evolution overpotential according to electrochemical compatibility (ECC) test.    USE - The microporous silica-filled polyethylene separator is useful in a lead-acid storage battery (claimed), which is useful in deep discharge cycle service and automotive starting-lighting-ignition service.    ADVANTAGE - The microporous silica-filled polyethylene low resistance separator improves electrochemical properties and performance of the battery, improves cycle life of the battery by controlling water loss during charge, and can be easily and economically manufactured with improved strength and mechanical integrity.    DETAILED DESCRIPTION - The microporous silica-filled polyethylene separator comprises cured rubber powder particles. The particles: have a low particle porosity (10%) and an antimony selectivity factor of greater than 1.10 as determined by the Antimony Suppression Test; contain an active ingredient, carbon black colorant and silica; and exhibit a low rate of diffusion of the active ingredient out of the particles and out of the separator through a controlled release mechanism and property of increasing hydrogen evolution overpotential according to electrochemical compatibility (ECC) test. The separator contains a mass ratio of cured rubber powder particles to polyethylene of 0.1-0.25. An INDEPENDENT CLAIM is included for a lead-acid storage battery.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a lead-acid storage battery.    Lead-acid storage battery cell (100)    Closed cell case (102)    Positive electrode grid (104)    Positive active material (106)    Negative electrode grid. (108)