The beneficial effects of pre-acclimation to a single low external resistor before a standard polarization test might be partially reversed while the EAB readapts to higher loads during the measurement. As well, the 1-to 2-hour relatively rapid cycle time between OCV and Rext could achieve long-term stability related to bacterial adaption to different currents during the polarization test. Another approach is in situ acclimation in which the polarization at each Rext is held for a long duration so that every point in the power density curve is fully and individually acclimated, thus achieving long-term stability. The accurate and constant flow from the microfluidic MFC eliminates nutrient cycling and the related voltage cycling that occurs in batch MFCs. Thus, microfluidic MFCs can provide a unique perspective on acclimation dynamics. We acquired the discharge curves during long-hold polarization tests with dwell times of up to 15 hours following the switch from OCV to selected Rext values, and each measurement was repeated three times at two different flow rates (QT=1 and 10 mL h -1 ). In all cases, the voltage stabilized at a minimum value over a relatively short timescale (termed t s ′ ). For Rext < 50 kΩ, the voltage eventually increased to a new (acclimated) voltage in a long time-scale stabilization (termed t s ′′ ). This time to adjust to high current demand is probably due the same effect involved in the current recovery observed previously in the power density curves near the end of the experiment. Both t s ′ and t s ′′ increased with decreasing Rext, but interestingly, applying higher flow rates reduced these times. As an example, Figures below show three discharge curves across external resistances of Rext=3.5, 30, and 300 kΩ. A plot of the measured t s ′′ as a function of