Just want to say thanks to all for taking the time to post the drawings which helps me a great deal as im no modder but can follow wires to + and - and also can solder
Everyone's a modder Dieseler...if you own a roll of duct tape, guess what...
...the LM2596 is a buck reg so you want to put your batts in series (wire them so that the pos of one connects to the neg of the other that way the the voltages of the batts add up, 3.7 + 3.7 = 7.4)...you're one hard core dude to
vape at 7.4v but when you wire that into the LM2596 reg input you can adjust it ("buck" it) down to say 5V or so...
...some guys (myself included) sometimes wire batts in parallel for DC (dual coil) carto's (wire them so the pos's of the two (or more) batts are connected, same thing with the neg's)...what you've done there is essentially doubled the capacity of your solitary batt...voltage is still only 3.7v but you've doubled the current output of what one batt can do and that set up will last twice as long as one batt would (this is all on paper of course, but that's the theory

)
Just wanted to add, batt boxes come pre set up in either a parallel or series configuration (or a combination of both), I wish the manufacturers would just give you a baggy of connectors but I digress, if you see a box you like (1, 2, 3, 4 batts, whatever) don't be afraid to grab it, I'm always pulling the batt connectors out of these boxes and re-jigging them to suit what I'm building, I just recently got two of the boxes used by Mamu for the Denali's (I'm gonna rip off the design cause it's good and that's how I roll, LMAO) but one of them is gonna be a parallel 18650 set up and one is gonna be a series vv