We constructed power density and polarization curves (Figures and) from long-hold polarization tests based on the voltages obtained after "virtual hold times", t s ′ and t s ′′ , each repeated for flow rates QT=1 and 10 mL h -1 . In all cases, Pmax was obtained at Rext=20 kΩ. At QT=1 mL h -1 , the Pmax value after hold time t s ′ was 346 mW m -2 (slightly lower but within the standard deviation of the average value (370 mW m -2 ) obtained from a standard polarization test following constant acclimation to 3.5 kΩ). This value increased to 383 mW m -2 under flow rate QT=10 mL h -1 . At hold times of t s ′ , absolute overshoot persisted, with ΔĪOS=205 (and the corresponding overshoot factor of ΘOS=24.5%) at QT=1 mL h -1 and 74 mA m -2 (ΘOS=8.5%) at 10 mL h -1 . In contrast, the overshoot was fully eliminated for power density curves that were constructed using voltages at t=t s ′′ from the polarization test voltage versus time profiles. In addition, Pmax and Īmax were improved (Pmax=405 mW m -2 and Īmax=1038 mA m -2 at QT=1 mL h -1 ), even compared to the pre-overshoot values obtained using the standard (non-acclimated) measurement protocol. Increasing the flow rate to QT=10 mL h -1 had a beneficial effect on Pmax and Īmax (Pmax=436 mW m -2 and Īmax=1215 mA m -2 ). Made possible by the microfluidic-assisted long-hold approach, in situ acclimation especially favours higher measurements of Ī at low Rext (including high values of Īmax), leading to an unusual shape of the curves in Figure . We do not believe that this shape is an artifact of the technique, but rather, it is the true form of a properly acclimated MFC. This view is supported by the similar Ī values obtained using the 4-day pre-acclimation approach at Rext=3.5 kΩ (before the subsequent standard polarization tests) and from similar power density curve shapes in multi-cycle acclimation conducted in bulk MFCs. (solid) and 10 mL h -1 (hollow). For eye guidance, solid and dashed lines indicate exponential fits for QT=1 mL h -1 and 10 mL h -1 , respectively. Reconstructed power density (e) and polarization curves (f) for total flow rates QT=1 mL h -1 (Δ) and 10 mL h -1 (•).