If you get the smaller vmod just get the 14500 batteries from vapage. If you get the xl I suggest the protected Panasonic 18650 3400mAh from FastTech. I'm a heavy vaper so I needed the higher battery capacity. The xl really isn't that big at all. Very pocket friendly...
The batteries are protected so if they fit the charger you should be okay. Investing in a good charger is never a bad idea though.
batteries
$16.21 Panasonic NCR18650B Protected Rechargeable 3400mAh 3.7V 18650 Lithium Batteries 2-pack - authentic cells / 2-pack / overcharge + over-discharge protection at FastTech - Worldwide Free Shipping
charger
http://www.fasttech.com/products/14...ore-i4-lithium-li-ion-ni-mh-ni-cd-smart-batte