tell me the science & math of why only the IMR.
Sorry to bring this back up, but I see you never got a quantitative answer. You don't necessarily need an IMR battery, but you
do need a battery that will safely and reliably provide the amps that the
mod draws. The exact amp requirement varies based on a lot of variables, but here's the worst-case scenario:
You're using a "standard" 510 atty that is on the low end of the ohm spectrum (2.2ohms), your battery is running low (3.2V) and you have the
mod set to 6V. Under these conditions, the mod will be pulling about 5.1 amps from the battery.
6V / 2.2ohms = 2.72A
2.72A * 6V = 16.32W
16.32W / 3.2V = 5.1A
If you want to play it safe, you should use a battery that exceeds this discharge rate. The AW IMR cells are definitely rated (and tested) for more than this, and that's why they're recommended. Other cells may be capable as well, but reliable data is hard to find. Many cells aren't labeled with a discharge rate (and some manufacturers lie). If you have cells that you know are good for at least 5 amps continuous discharge, they should be fine. If you don't know what your 18500/18650 cells are rated for, you're better off upgrading to something you know will work.