Notably, at identical source concentrations of 1 M (pH 0 and pH 14 for protons and hydroxide ions, respectively), the proton crossover flux through DSV-N is almost two orders of magnitude greater than hydroxide crossover flux through E620. As a result, concentrated acid solutions should be used with particular caution in order to avoid energy costs and the lifetime penalty associated with proton crossover in pH-decoupled ARFBs. We hypothesized that rapid crossover can be prevented while maintaining high cell voltage through "mild" pH decoupling. Operation at pH 13 and 3 (a difference of 10 pH units) can still allow an OCV higher than 1.7 V if the negolyte and posolyte are chosen appropriately, as seen in Fig. . By using milder acid and base than previous pH-decoupling batteries, we can still achieve relatively high voltage while exponentially reducing the unwanted acid-base crossover, thus approaching an optimal balance in the tradeoff between operating voltage vs. energy inefficiency and instability due to crossover.