A non-woven sheet of polyolefin fibers having opposed major surfaces is disclosed. Some areas of one or both of the major surfaces are hydrophilic as a consequence of an acrylic graft polymerized with the surfaces of the fibers in those areas while the fibers in other areas of that major surface are free of the graft and, as a consequence, remain hydrophobic. A battery separator composed of at least two such non-woven sheets is also disclosed, as well as batteries having a separator composed of at least one such non-woven sheet. Also disclosed is a non-woven sheet of polyolefin fibers where opposed major surfaces of the sheet are hydrophilic as a consequence of such an acrylic acid graft, but the ion exchange coefficients of the two major surfaces are different.