I forgot to add if your interested in the ecig like stick batteries, the 510 and Kr808 is the ones popular now, then you can buy empty cartomizer tubes, cheaper then refills and refill them more than once yourself using any liquid you prefer.
the only problem is the battery life is somewhat lacking.
a slightly larger battery like an ego style will give you more charge life and open you up to a wider assortment of accessories without having to upgrade the battery down the road. the days of 1 or 2 addones is over there are 100's of different things we can now screw on to our batterys, carts,
tanks even rebuildable systems.