Polymer electrolyte membranes (PEM) are a key component in many fuel cells and in redox flow batteries (RFB). So far in most applications Nafion membranes are utilized. In search of alternate membrane materials various approaches are pursued. One of them is the radiation-induced activation of polymer films and subsequent graft copolymerization [1]. In this contribution the preparation of PEMs in a three step process is reported: Firstly, commercially available fluoropolymer films, e.g., poly(ethylene-co-tetrafluoroethylene) (ETFE), are activated via electron beam treatment. Secondly, graft copolymerizations with functional methacrylates, e.g., such as hydroxyethyl methacrylate and glycidyl methacrylate, are performed. Then, the functional groups are sulfonated yielding the final PEM. Alternately, copolymerizations may be carried out with acrylic acid and hydroxyethyl acrylate, and subsequently the material is phosphonated to yield proton conductivity. The impact of the ETFE activation process, in particular the adsorbed dose, on the grafting process, and consequently the performance of the PEM is addressed. In order to reduce cross-over in vanadium redox flow batteries the polymerizations may be carried out in the presence of crosslinkers. The electrical performance of the resulting membranes is evaluated by electrochemical impedance spectroscopy as well as in fuel cell and in VRFB tests. In the latter up to 300 charge and discharge cycles were carried out, lasting for nearly a month. Stable electrochemical performance directly indicates membrane stability under typical VRFB conditions [2]. [1] L. Gubler, Adv. Energy Mater. 2014, 4, 1300827 [2] X. Li, A. R. dos Santos, M. Drache, X. Ke, U. Gohs, T. Turek, M. Becker, U. Kunz, S. Beuermann, J. Membr. Sci. 2017, 524, 419