NOVELTY - A microporous polymeric membrane has a surface comprising micro-fibrils having an average diameter of 20.0-1.0x 102 nm and an average distance between micro-fibrils of greater than 400.0 nm.    USE - A microporous polymeric membrane for use in a battery separator film of a battery for use as a power source for a power tool, electric vehicle or hybrid electric vehicle (claimed).    ADVANTAGE - The microporous polymeric membrane has a normalized pin puncture strength of greater than or equal to 20.0 gF/ mu m and a normalized air permeability of less than or equal to 11.0 s/100 cm3/ mu m. It has a transverse direction (TD) heat shrinkage at 105.0 degrees C of 3.0-10.0% and a machine direction (MD) heat shrinkage of 1.5-8.0%, a porosity of 45.0-50.%, an MD tensile strength of greater than or equal to 1.0x 103 kg/cm3, a TD tensile strength of greater than or equal to 1.2x 103 kg/cm3, an MD tensile elongation of greater than or equal to 50.0%, a TD tensile elongation of greater than or equal to 50.0%, a shutdown temperature of less than or equal to 140.0 degrees C, a meltdown temperature of greater than or equal to 144.0 degrees C, a maximum MD heat shrinkage in the molten state of less than or equal to 41.0%, and a maximum TD shrinkage in the molten state of less than or equal to 46.0%.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a battery separator film comprising the microporous membrane;    (2) a method for manufacturing a microporous membrane comprising stretching an extrudate comprising 60.0-80.0 wt.% liquid paraffin and 20.0-40.0 wt.% polyolefin mixture in planar direction; removing at least a portion of diluent from stretched extrudate to produce a dried extrudate; and stretching the dried extrudate to a larger width by a magnification factor of greater than or equal to 1.3 while exposing to 126.0-131.0 degrees C and maintaining the dry length; and    (3) a battery comprising an anode, a cathode, an electrolyte, and separator between the anode and the cathode.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph of the relationship between normalized pin puncture strength and normalized air permeability for selected microporous membranes.