On my first pair of 20700b batteries I consumed 28 - 29 ml of eliquid, at 25w, before deciding to change batteries. The PD270 hadn't generated a low battery warning yet, though it had been showing only 20% charge on the batteries for a while. Per my charger the batteries were fine, evenly discharged, 3.5v (I must have been right near cutout).
Phenomenal runtime, consistent performance throughout [emoji3]