TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The planar direction is TD and the membrane has heat shrinkage at 105 degrees C in at least one planar direction of less than or equal to 2.5%. The polyolefin comprises a first polyethylene, and further comprises at least one of polypropylene having an Mw greater than 1x 106, or a second polyethylene having Mw greater than 1x 106. The first polyethylene has Mw of 1x 105 to 9x 105 and MWD of 3-15, the second polyethylene has Mw of 1.1x 106 to 5x 106 and MWD of 4-20, and the polypropylene has Mw of 1.05x 106 to 2x 106, MWD of 2-6, and Delta Hm greater than or equal to 100 J/g. The polyolefin comprises: the first polyethylene (60-99 wt.%) and the second polyethylene (1-40 wt.%). The polyolefin comprises: polypropylene (1-50), the first polyethylene (25-99 wt.%), and the second polyethylene (0-50 wt.%). The polypropylene is an isotactic polypropylene having an Mw of 1.1x 106 to 1.5x 106, and a Delta Hm of 110-120 J/g. Preferred Method: In the method, the MD and TD stretching are each conducted to a magnification factor of 3-9 fold while the extrudate is exposed to a temperature during stretching in the range of Ted to Tm. The method further involves heat setting the membrane following membrane stretching step and reducing step. During membrane stretching step the MD stretching is conducted before the TD stretching, where the first magnification factor is greater than the second magnification factor, and where the MD stretching is conducted while the membrane is exposed to a first temperature of Ted-30 degrees C to Tm-10 degrees C; and the TD stretching is conducted while the membrane is exposed to a second temperature that is higher than the first temperature but lower than Tm; and where the reducing is conducted while the membrane is exposed to a temperature greater than the second temperature. Preferred Battery: In the battery, the electrolyte contains lithium ions and the battery is a secondary battery. EXAMPLE - The monolayer microporous membrane comprising polyolefin composition containing first polyethylene resin (70 wt.%) having Mw of 5.6x 105 and MWD of 4.05, and polypropylene resin (30 wt.%) having Mw of 1.1x 106, MWD of 5, and heat of fusion of 114 J/g, was prepared. The obtained monolayer microporous membrane shows thickness of 21 mu m, porosity of 42%.