A battery comprises a separator membrane comprising an ion-conducting polymeric composition comprising a copolymer of R.sub.a-R.sub.s and R.sub.b. R.sub.a and R.sub.b are each selected from the group consisting of linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls, heteroaryls, alkylaryls, and heteroalkylaryls. R.sub.s is a positively charged amine group or a positively charged phosphene group. The copolymer comprises at least 3% of each R.sub.a and R.sub.b by weight. R.sub.a and R.sub.b are different chemical constituents, and R.sub.a-R.sub.s is not vinylpyridine.