A battery separator for a lead/acid battery is resistant to oxidation arising from the use of water or acid containing contaminants, for example chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), and the like. The separator is a microporous membrane including a rubber. The rubber is no more than about 12% by weight of the separator. The rubber may be rubber latex, tire crumb, and combinations thereof. The rubber may be impregnated into the microporous membrane. The microporous membrane may be a microporous sheet of polyolefin, polyvinyl chloride, phenol-formaldehyde resins, cross-linked rubber, or nonwoven fibers. A method for preventing the oxidation and/or extending battery life of the separator is also included.