I just found this thread. It looks really interesting.
Welcome aboard!
Well, it seems like the battery preferences depends on indended usage. On one hand, if you use more than a single 18650 in a day, the move to a 2x700 battery is pretty much a no brainer. On the other hand, if you can get away with a single 18650 in a day, sticking with 18650 starts to make more sense...
I am still up for making both sizes, the tooling change is very minimal.
It's been interesting to test the heater modules... being unregulated there is definitely a lot to consider with the dropping battery voltage...
Personally I am starting to like the heaters that I can hold the trigger down constantly, and regulate temperature with draw speed only. Meaning, the surface area is great enough that the heat can be taken away faster than it can accumulate. I can overpower the heater with a fast draw speed.
This sort of heater will start out, on a fresh 4.2v battery, being able to overpower draw speed, just barely. Meaning that if I keep holding the fire button down, I will eventually scorch the load, even at a fast draw speed.
But by the time the battery has settled down around 3.7v, a medium draw speed is required for proper temperature. A fast draw speed can over-power the heater and give a temp that's too low.
With medium draw speed, you can have the fire button on for the entire draw.
Because I like vaping pipe tobacco, I prefer a slower draw speed, I feel like this gives the thick flavourful vapor I expect to get from a pipe, more time for the vapour to flowww out and move around the mouth.
This style also seems to be best for newcomers, and in group sessions, very easy to control and get the correct temp without overshooting, no fire button modulation required.
But I can definitely see the advantage of a heater that is NOT overpowered by draw speed, even at 3.7v. For more experienced users. At 3.7v, this will act more like the above heater at 4.2v.
neat stuff!