We then conducted a polarization and galvanostatic analysis of the optimized cell structure with a negolyte composition of 0.1 M BHPC at pH 13 (10 mL) and a posolyte composition of 0.1 M Fe(Bhmbpy)3 at pH 3 (4.5 mL). The potential was held at the end of discharge in order to recover Fe(Bhmbpy)3 from dimerization. Polarization curves and galvanic power densities are shown in Fig. . The three-chamber pH-decoupling battery reached a peak power density of 140 mW cm -2 at 80% SOC. Fig. shows the OCV of the cell, increasing from 1.69 V at 20% SOC to 1.8 V at 90% SOC. The high-frequency area-specific resistance (ASR) of the battery averaged 2.85 Ω cm 2 while the average polarization ASR across all SOC was 3.82 Ω cm . These values indicate that most of the cell's overall resistance is attributable to the resistance of the membranes. Fig. depicts the voltage profile of the cell at different current densities, from which we extracted the Coulombic efficiency, capacity utilization, and round-trip energy efficiency for Fig. . At 40 mA cm -2 , this high-voltage cell exhibits 80% round-trip energy efficiency, which indicates that voltage losses are minimized due to the optimized design of the three-chamber cell. Because power output and overall ASR appear to be essentially dictated by the resistances of the two membranes, further development of lower-resistance CEMs and AEMs with high selectivity is a high priority for future research. 24 To gain insight into the future development of such pH-decoupling systems, we studied the cost penalty from acid-base crossover. The capital cost was estimated using a reported technoeconomic model, reckoning the additional costs associated with a three-chamber two-membrane setup and a pH recovery system. By assuming a BPM sub-cell that operates at a steady-state current density for pH recovery, higher crossover leads to higher capital cost associated with a larger BPM subcell. This also results in higher energy cost for pH recovery, penalizing the roundtrip energy efficiency (Fig. ). Acid-base crossover will be less impactful when using a battery stack with smaller area and higher current density. Because the required battery area for a certain power output decreases roughly as (ASR) × (OCV) -2 , an increased OCV cuts the rate of acid-base crossover and thereby cuts the BPM cell cost and the energy efficiency penalty of the recovery system. This makes the costs of the recovery system acceptable if the increased OCV more than With this mild pH-decoupling setup with pH recovery, exhibiting a crossover flux smaller than 0.3 nmol s -1 cm -2 , we have a negligible energy and capital cost penalty due to the recovery system. Thus, we have realized the first long-term practical pH-decoupling ARFB, theoretically permitting an indefinite duration of operation and demonstrating dramatically longer operation with slower fading compared to previous examples, as illustrated by the duration of stable cycling reported in Fig. . We report this comparison to emphasize that future pH-decoupling cell designs should place a greater focus on long-term operation possibility and technoeconomic considerations. Higher voltage output, as already demonstrated in previous works , can be beneficial because it lowers the cost related to pH recovery and therefore, can make higher acid-base crossover rates tolerable. But researchers should be careful when using concentrated acid (> 1 M protons) for its large crossover flux. To ensure optimal performance of a pH-decoupling cell with an OCV around 2 V, pH crossover is better to be limited to less than 200 nmol s -1 cm -2 (equivalent to a leakage current density of 20 mA cm -2 ).