@KenD
Your first post "Two 18650s will be able to handle more current" is what I was referring to.
Two 20A CDR batteries in parallel would deliver 40A CDR where as in series only 20A CDR.
While your examples are correct I disagree with "Parallel or series doesn't matter in a regulated setup". There is more to the story and more examples.
Example 1:
two cells in series: 7.4V supply drawing 10A - delivered to atty: 7.4V at .1ohm and 10A is 74W
Example 2:
one cell 3.7V supply drawing 20A to Boost to 7.4V - delivered to atty: 7.4V at .1ohm and 10A is 74W
With example 2 the run time is halved assuming same maH ratings, but 26650s have more capacity which is a reason to go with 26650 versus 18650 for a single cell mod with boost ie Slice.
Also Example 1 can use two 10A CDR batteries. Example two would need a single 20A CDR battery.
Example 3 (0.1ohm atty): At 101W, the current would be 31.76A, and 3.18V at atty. There are no 31.76A CDR 18650s or 26650s so in dual series mods like the G2, it can't get 101W CDR @0.1ohm.
Example 4 (0.1ohm atty): However, there are plenty of 18650s and 26650s that will supply more than half 31.76A CDR or 15.88A, as in two 20A CDR in parallel. So a dual 20A CDR parallel mod with buck down from 3.7V to 3.18V can get to 101W CDR.
Yes I too am ignoring inefficiencies and also pulse, only talking CDR.
And yes I have made a quad .4ohm parallel build that yields .1ohm total and vaped it at 100W.
The point is, both example 3 and 4 are regulated mods, the mod with two in series cannot get there even with adding more batteries but a mod with two batteries in parallel can.
There are other examples at high resistances where more source voltage ie series, and/or with boost where they can get there but parallel cannot.
But these alone clearly prove series versus parallel does matter.
HTH