I vape 1 ohm coil on fresh batt and that's about 16 watts of power and that goes down as batt life goes down, and I change out batt at about 3.7 volts (now I'm under 16 watts) If I purchase a 75W device, and I set it at 75 watts is that what I get regardless of the build of my coil, does coil build even enter the conversation since I can set power at whatever I want. I don't want to purchase power that I'm not going to use. Thanks for your help.
If you have a Regulated Variable Wattage (VW) Device, then yes, whatever Wattage you set it at will be the Wattage that the Device provides regardless of the Ohm of you coil.
So if you put a 1.0 Coil on a Regulated Mod and then set it for 16 Watts, the Mod will do the Math to Calculate what Output Voltage is needed to make 16 Watts with that 1.0 Ohm Coil.
Now you switch to a 1.2 Ohm Coil. The Mod will do a New Calculation and change the output Voltage to maintain 16 Watts for your 1.2 Ohm Coil.
And for whatever Ohm you use and Wattage that you set the Mod at, the Hit you get will be the Same for a Fresh Battery or for a Partially Drained Battery or for a Battery that is at 3.7 Volts.
So No More it hits a Little "Hot" with a Fresh Battery. And it hits a Little "Weak" with a Battery that is Drained. You also can Try Different types of Ohms/Builds and find where they Hit Best by just Adjusting the Wattage on the Mod.
Buying a 75 Watt Regulated Mod even if you only use around 16 Watts (on average) isn't really Buying more than you need. Because the Price now is more based on other Features and Popularity than on the Total Watts.
If your thinking of getting a New Mod, I would suggest that before you buy it, to post what you are considering getting in this thread. Because there are some Mods like the DripBox 60W make it sound like they maintain 60 Watts no matter what build you put on them. But they Don't. And they work more like your REO.