Disclosed are battery separators comprising glass fibers and having a basis weight (gsm), a specific surface area (m2/g), a density (gsm/mm) and a mean pore size (μm), which satisfy the equation disclosed herein, provided that: the specific surface area is less than 1.5 m2/g, or the density is greater than 180 gsm/mm. Also disclosed are batteries comprising the battery separators, and processes for making the separators.