Novel or improved microporous battery separator membranes, separators, cells, batteries including such membranes, separators, or cells, and / or methods of making such membranes and / or separators, and / or methods of using such membranes and / or separators. In accordance with at least certain embodiments, an improved or novel battery separator for a secondary or rechargeable
lithium battery may have low Electrical resistance of less than 0.95
ohm-cm2, or in some cases, less than 0.8
ohm-cm2. Furthermore, the inventive battery separator membrane may provide a means to achieve an improved level of battery performance in a rechargeable or secondary
lithium battery based on a possibly
synergistic combination of low Electrical resistance, low Gurley, low
tortuosity, and / or a unique trapezoid shaped pore. In accordance with at least certain multilayer embodiments (by way of example only, a trilayer membrane made of two
polypropylene layers with a
polyethylene layer in between), the inventive microporous membrane or battery separator may have excellent onset and rate of thermal shutdown performance.