Which batteries should I use, and where should I buy them?
Battery information guideIf you're using 18650s in a regulated device, your best bet is the Samsung 30Q, Sony VTC6, or the LG HG2. If those aren't available, the Sony VTC5A, LG HE4, or Samsung 25R are the next best thing.
Only Sony, Samsung, LG, and Sanyo make their own batteries. All other companies aren't manufacturing batteries. They are providing rewrapped versions from one of the aforementioned big four and youshould not buy them as what battery is under that wrap can change at any time and may certainly not be appropriate for vaping. Furthermore there is no regulation of batteries and most of those rewraps have fabricated ratings of amps and mah.
As far as where you should buy those batteries from, the preferred trusted vendors are IMR Batteries, Illumn and Liion Wholesale. All are trustworthy, have good prices, and test random samples to ensure they are authentic. It's also a good idea to pick up some replacement battery wraps as well as insulators to have on hand. They're dirt cheap, and can greatly extend the lifespan of your batteries as the wrap is usually the first part to get damaged.