the bigger the battery the longer it lasts, if everything else is equal. so for a GGTS, the 18650, and the AW2600 18650 is going to be the best and longest lasting battery the device can hold (factoring cost and protection circuitry, etc.). in theory, a 3.7V battery in any size should give you the same perfromance, the only difference being the length of the performance. but, because all batteries aren't created equally, and smaller batteries suffer from insufficient amperage (among other manufacturing quality and safety issues) to drive the atomizers that we use, you'll want to be very careful about the batteries you select for anything below an 18650. now, the GGTS handles everything, goes from short to tall, but it cannot change it's diameter...so using a 16340 (16 or 17 mm wide) is a waste, and you'll want to stick with 18*** batteries because they'll maximize the space, afford a battery with greater stored energy and ultimately better runtime. so get an AW IMR18350, because your other options in that size will not perform as efficiently. the next step up is an 18500 or 18490 (IMR), you can go with either, but like the 18650 the AW18500 is also able to handle the amperage drain of pretty much everything out there...anything under 3 Amps, but if you need a battery for both VV and regular use and something that may push beyond 3A, go with the IMR18490 instead. Next stop is the 18650 which you're zeroing in on now. so despite the ability to use however many types of batteries, there's really only three or four (if you're stacking for 6V instead of 7.4V) that you need to worry about.
