And why the Provari?
It provides an Atmistique voltage meter, you clip it onto the 510, the atomizer on top, and it measures what voltage the mod pushes out under load, meaning how much the battery drops under load.
Provari with 4.1 Volts output in idle:
And Provari with the 1.6 ohm Taifun under load:
And this is a 13-year-old device, with intensive daily use… 
Even Daniks drop more than this (0.04-0.1 V)…