Abstract: A battery separator for tubular positive electrodes composed of a microporous, composite sheet product having first and second major surface, formed from a uniform mixture of a polymer, a filler, a processing aid a porous form stable layer at least partially embedded in either the first or second major surface and having a series of vertical tubes arranged across its surface. The tubular sleeve/separator can be formed of individual tubes, flat sheets formed into a series of tubes or sheets containing half tubes and which are aligned and bonded together to form the series of tubes.