I’ve been vaping for a couple years now and have decided to get into mech mods. I’m doing my research on Ohm’s Law to being but I’m a bit confused by the Voltage Input part. When I’m calculating my amp draw do I use the 4.2V that my battery outputs raw, or do I use the 3.2V that I get after doing my voltage drop test?

Welcome. If your voltage sag is that huge, then something tells me you must be doing something awful wrong... either the reading is way off, or you are using a shitty battery, or your ohms are much too low, possibly it's a combination of these factors. What you call "raw output" is the resting voltage, which typically equals 4.2 volts if the battery is fully charged. The running voltage, or voltage that the battery runs at, equals the resting voltage minus the voltage sag. Use the running voltage for your Ohm's law calculations, but first, be sure to also understand how much voltage sag you will be getting from the battery you use. You can look at Mooch's pulsed current discharge graphs for that, and notice how the voltage sag is different depending on how many amps are drawn from the battery, and also notice how it's different for different batteries as well. Mooch wrote that these graphs will soon be replaced with number data. But for now, it's basically all we have. If you are looking at a single 18650 battery tube mod, I recommend going for the Sony VTC5A battery (not to be confused with the VTC5).

That's a lot of drop. Maybe pushing the battery too hard and getting excessive voltage drop. But for calculating your actual wattage at your atty use the 3.2 V number. This post is based on assuming that you are using a mech.

Wont hurt to add a few 0.1 volts to what you think the voltage sag is too for calculating ....not all cells are made equal even the good ones, so some might dip further than others or likewise less

Keep in mind the more voltage sag from a battery the hotter the battery runs and heat buildup is what causes thermal runaway/venting.

Yep I noticed early in my vape journey that AW & Efest get very hot quite fast.If I recall I was using a Vamo2 at the time.It concerned me and when I mentioned it at a vape forum (Ecig Advanced) I was told to order some Sony or Samsung batteries/cells.And to toss all my AW & Efest batteries as soon as the Sony's or Samsung's arrived.I have stuck with those brands and have had zero issues since.