NOVELTY - The multi-layer microporous membrane comprises first and third layers, and a second layer located between the first and third layers. The membrane has a transverse direction (TD) of 105 degrees C heat shrinkage of less than or equal to 0.25% in a planar direction, and a normalized air permeability of less than or equal to 400 second/100cm3/20 mu m. The membrane has a machine direction (MD) maximum shrinkage in the molten state of less than or equal to 10% and a TD maximum shrinkage in the molten state of less than or equal to 20%. The second layer is in planar contact with the first layer and the third layer. A total thickness of the membrane is 3-200 microns.    USE - The multi-layer microporous membrane is useful in a secondary battery, which is a source or sink of power to the components including unit for moving an electric vehicle or hybrid electric vehicle (all claimed), where the battery further includes primary and secondary lithium batteries, lithium polymer batteries, nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries and silver-zinc secondary batteries and useful as a battery separator film.    ADVANTAGE - The multi-layer microporous membrane has improved heat shrinkage properties, permeability and strength and better dimensional stability at elevated temperature, and provides excellent safety, heat resistance, retention properties and productivity to the batteries.    DETAILED DESCRIPTION - The multi-layer microporous membrane comprises first and third layers, and a second layer located between the first and third layers. The membrane has a transverse direction (TD) of 105 degrees C heat shrinkage of less than or equal to 0.25% in a planar direction, and a normalized air permeability of less than or equal to 400 second/100cm3/20 mu m. The membrane has a machine direction (MD) maximum shrinkage in the molten state of less than or equal to 10% and a TD maximum shrinkage in the molten state of less than or equal to 20%. The second layer is in planar contact with the first layer and the third layer. A total thickness of the membrane is 3-200 microns. The second layer has a thickness of 5-15% of the membrane's total thickness. The thickness of the first and third layers is 42.5-47.5% of the membrane's total thickness. The membrane has a normalized permeability of less than or equal to 300 second/100 cm3/20 mu m, porosity of greater than or equal to 25%, a normalized pin puncture strength of greater than or equal to 2000 mN/20 mu m, an MD tensile strength of greater than or equal to 90000 kPa, an TD tensile strength of greater than or equal to 75000 kPa, MD tensile elongation of greater than or equal to 50%, TD tensile elongation of greater than or equal to 50%, a rupture temperature of greater than or equal to 170 degrees C, a shutdown temperature of less than or equal to 140 degrees C, less than or equal to 20% of thickness variation ratio after heat compression, less than or equal to 1000 sec/100 cm3 of air permeability after heat compression, and a surface roughness of greater than or equal to 2x 102 nm. INDEPENDENT CLAIMS are included for:    (1) a method of producing a microporous membrane; and    (2) a battery.    DESCRIPTION OF DRAWING(S) - The diagram shows a perspective view of a cylindrical type lithium ion secondary battery.    Anode sheet (12)    Cathode sheet (13)    Cathode lead (21)    Insulation plate (22)    Battery can. (23)