Thanks all except Atty Pops. You must reread my post and see that I did not intend on 'using' a stacked battery system in anything; I simply wanted to be educated instead of someone being condescending. Do not reply in that manner as you may turn a potential new vaper away by sounding pompous.
You have me wrong. I read your post and knew that you didn't intend to.
I guess the point is, for you and for others, what purpose would it serve? (It was a rhetorical question)
As to sounding pompous, I don't read it that way at all. Also see post #3...I stack batteries, but under specific circumstances.
What manner did I reply in that offended you? You're reading something into it that is not there. Post #4 was elaborating on the last sentence in post #3...basically the idea is that you don't need to stack because there's other ways of getting the same watts without the stacking dangers. Which was sort of your question.
Simple question, and no, I'm not trying or thinking of trying this. I just want reputable information. so I can educate myself and others. Why exactly can you not stack two 18350 batts in an 18650 mech mod?? Please take it easy on meh. Like I said, I'm not experimenting with this, just curious why???
Basically, you [people] can, but it's less safe and you [people] don't need to do that in a mech, as there are better ways.
Also note that "you" in American English (informally) is often used generically, as in "a someone", not necessarily being YOU personally but rather "a person". At least I often use it that way.

As in "You can, but why would you want to?" It's really "A person could, but why would anyone want to?" See? You even seem to use it that way in your question. Although the way I phrased it could be misconstrued if you didn't notice my previous post.
I meant it generically, as in "Why would anyone wish to stack batteries in a mech mod?"
In the "old days" people DID stack them. They didn't have RBA's and coil wire around. They used stock coils and high-ohm stuff designed for higher voltage vaping. Now-a-days, we use the single battery approach. Basically, higher-voltage vaping had more "oomph" to it. I used to use 5 volt regulated (fixed voltage) box mods with stacked batteries and 3.0 ohm atomizers, for example. Others, stacked batteries and used, say, 4.x ohm atomizers in unregulated mods.