Cross-linked quaternary ammonium functionalized Radel membranes with a high degree of functionalization (DF) were synthesized and evaluated in a vanadium redox flow battery. The permeation of vanadium cations through this type of anion exchange membrane was reduced significantly compared to sulfonated ion exchange membranes, while the ion conductivity of the AEM was low. Increasing the DF increased the ion conduction and crosslinking endowed mechanical strength in water by restricting swelling. However, crosslinking decreased the ion conductivity of the membrane, which offset the benefit of increasing the DF and the very low vanadium permeation. The resulting cell performance was similar to that of N212.