Congrats, Ramaview, and welcome to the 'Ville
The grand will handle most any 18650 bat, but there are a couple of things to consider:
* if you have the older bat spring and firing pin (they're silver, the newer ones are gold), you prolly want to stick with button tops. There is a chance that you could get arc'ing to the bat. This can be alleviated with noalox on the battery and firing pin.
Thanks. Will get some
* you want a battery that's safe for the way you vape, specifically, that it is rated for the draw (amps) that you need. This is a function of the coil(s) that you run on the unit. Basically, divide 4 by the ohms of your coil to determine the needed amp rating (plus add some head room just for added safety). E.g., a 1.0 ohm coil will result in a ~4 amp draw (4 / 1.0), a .5 ohm coil will result in 8 amps, and so forth. Add the headroom, and you you're looking at needing, say, 6 amp bats for the first example, and 10+ amp bats for the second.
So, for these (and other) reasons, most folks like the AW 1600 mah bats and the Sony VTC5's (the latter being flat top, however).