Edit: VV = variable voltage. VW = variable watts. You can find another thread or ask more on those specifically. It's a common question and thought I should at least clarify abbreviations since you look like a new member.
I couldn't find a dedicated battery sub forum, so I guess this one will have to do. Maybe I'm just blind, if so then I request a mod please move this to the correct forum for me. But as batteries are a major part of any mod, I figured this may be as good a place as any.
So here are the questions, some unrelated to thread title.
1. Are two 18350's better than 1 18650? I recently saw a youtube vid where a guy was reviewing a mod, and he said that it just works so much better with dual 18350's. As opposed to a single 18650. Why would this be? Could this also be the case, with all other mods?
Dual 18350's are running batteries in a series. Look up series vs parallel battery circuitry if really curious. You are effectively doubling the voltage. Given the resistance of your atty is constant you are doubling the hotness and vape. This would probably only affect a mechanical mod and someone correct me if wrong. Most mods that come with circuitry such as vamo or provaria, etc there is no need for this as you control the variable voltage and/or variable watts on your own. So I can really only see this helping in mech mod and maybe when getting into the sub ohm resistance atties.
Side note you run higher risk of battery failure when running Li-Ion batteries in series. The term I have heard is that you are "Marrying" the batteries. Those two batteries can only be used together, should be charged together, and should be alternated from top to bottom each time. Ie if B1 goes in first and B2 goes in second. After charging B2 needs to go in first and B1 goes in second. This is to help balance and the battery life and prevent one from causing a thermal meltdown.
2. Why are people such fans of those 1600mah AW 18650's? Don't they run out of battery life too fast? My Panasonics are 3400mah, so why wouldn't people just but the (reputable) ones that are the highest mah? I'm a chain vaper, so even my 3400mah Panasonics only last me a little over 1 day's worth of vaping.
I'll defer to more knowledgeable poster but the mah is somewhat subjective. Also the AW and IMR can have high drain loads. Meaning they can put out more amps per second without overheating. Some the higher rated mah batteries don't have a high drain rate meaning that they last longer but may not be putting out the required amps you device is requiring at your VV or VW setting.
3. Why would you choose one coil, over another? Why would someone choose to use a 1.3ohm coil on one build, only to use a 2.5ohm coil on another, different build? What is the purpose of choosing lower or higher ohms?
Say you don't have a Variable Voltage VV or Variable Wattage device. Say you just got standard Ego battery. Well the only way to change the heat/vapor amount is to decrease the resistance of your atty. Higher resistance the longer the battery life but the cooler the vape. Lower the resistance the less the battery lasts but the hotter/cloudier the vape.
I bought several different attomizer/tanks when starting out when I only had an ego. After switching to a vamo and also use VV passthrough it probably doesn't matter as much as you can dial in on the "heat" you want. I started with VV but personally have found like VW better. Main reason is I have different tanks with different resistances from my original purchases. VW allows you to choose the "heat" regardless of resistance. The device calculates the resistance of your attached attomizer and puts out the appropriate voltage. When using VV if you change your tanks you have to redial in quite a bit more as you need more volts with higher resistance to equal the same "heat" and need less volts with lower resistance atty to equal the same amount.
VV and VW are really the same thing it's just different roads to the same end goal and I find VW works better for my setup since I have a wide variety of resistance in my atty and tanks. If all of your tanks/atties are same resistance VW will give you probably no benefits as when you switch tanks you don't need to recalculate your voltage...well other than fact that atties can change resistance over time...but still either do the same thing just different calculations and different methods.
Also as for higher vs lower ohm coil. I prefer a stronger throat hit / hotter vape in the morning. So would use a lower resistant coil in the morning. I like a smoother less harsh hit in the evenings so preferred a higher ohm coil during those times. When you start using VV or VW you care not so much about the coil but the voltage or watts. So no more need to change resistance you just push a few buttons up or a few buttons down to get you to where you want to be.
Also with standard ego's they gradually lower in voltage over charge cycle so your vape becomes gradually weaker until you recharge your battery to max.
I'm sure others can help explain better but thought I'd give a stab at your questions.
