NOVELTY - A microporous membrane comprises: a first polyolefin (A1) ( greater than or equal to 1 wt.%) having a temperature (T80) at which the crystal-melting calorie Delta Hm measured by melting distribution (DSC) at temperature-elevating speed of 10 degrees C/minute reached 80% of total Delta Hm of less than or equal to 130 degrees C, a temperature (T25) at which the crystal-melting calorie Delta Hm measured by DSC at temperature-elevating speed of 10 degrees C/minute reached 25% of total Delta Hm of greater than or equal to 100 degrees C, and T80-T25 of less than or equal to 25 degrees C.    USE - In battery separator useful in battery (comprising lithium ion secondary battery, lithium-polymer secondary battery, nickel-hydrogen secondary battery, nickel-cadmium secondary battery, nickel-zinc secondary battery and silver-zinc secondary battery) (claimed) as a power source in e.g. electric vehicle, hybrid electric vehicle, power tool, computer, mobile phone and consumer electronics.    ADVANTAGE - The microporous membrane has a shutdown temperature of less than or equal to 130.5 (preferably 120-130, especially 124-129) degrees C; and has a normalized air permeability less than or equal to 6 x 102 seconds/100cm3/20 mu m, a normalized pin puncture strength greater than or equal to 1.5 x 103 gf/20 mu m, and a 105 degrees C heat shrinkage in transverse direction (TD) of less than or equal to 10% i.e. has well-balanced permeability, shutdown temperature, and pin puncture strength i.e. has relatively low shutdown temperature and relatively air permeability and high strength.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) making a microporous membrane involving: (a) extruding a mixture of diluent and polymer, the polymer comprising a first polyethylene (1-20 wt.%) having a T80 less than or equal to 130 degrees C, T25 of greater than or equal to 100 degrees C, and T80-T25 of less than or equal to 25 degrees C; (b) stretching the extrudate in at least one planar direction; and (c) removing at least a portion of the diluent from the stretched extrudate; and    (2) a battery comprising an electrolyte, an anode, a cathode, and a separator situated between the anode and the cathode, where the separator comprises first polyolefin (A1) ( greater than or equal to 1 wt.%); the separator having a shutdown temperature less than or equal to 130.5 degrees C.