We extended the advantage of the long-hold polarization test to construct and investigate power density curves at arbitrary hold times of t < t s ′ (i.e., to investigate the effect of polarization tests that were too fast). Power density curves from discharge curves obtained under QT=1 mL h -1 using virtual hold times of 2 hours or less were chosen to mimic standard polarization test conditions used in this work (Supplementary Materials, Section S7). The longest hold time was 2 hours (t≈t s ′ ) and resulted in a power density curve that was nearly identical to the constructed power density curve in Figure for t=t s ′ (QT=1 mL h -1 ). This was expected because 2 hours was sufficient to obtain short-term stability. This "stable overshoot" does not represent a measurement error because stability was achieved, but it does represent an error in experimental design because it did not account for the voltage recovery after long-term stability was reached. A 90-minute hold time resulted in a worse overshoot (type D), and a further reduction in the hold time to 60 minutes caused a drop in power density near the apex of the power density curve, similar to that (type M-like overshoot) observed in Figure after t=45 days.