A 1300 mah Spinner. Or else something with replaceable batteries. I decided my LT was too long and just bought a gripper, but really, I like the Spinner best...except it seems more "green" (and a little bit less trouble) to use replaceable batteries, then I don't have to unscrew the head when the battery runs out. But those are all a LOT bigger for the performance than the 1300 mah Spinner, which lasts all day, maybe longer. 2 of those and you're done.
However, the place where upgrading REALLY matters is the top, not the battery (assuming you have vv or vw)
I'm on the Vision Vivi Nova but I've heard there are better clearos out there. Still have not heard of one that NEVER leaks, though, the best I hear is "Well, hardly ever." I guess I'll stick with my Novas but I'd really like something that vapes the same but is leak-proof ALWAYS, and never pushes the post on my battery down too far, and can't easily get cross-threaded. AND has a replaceable sleeve inside -- people say you don't need that little woven fiberglass sleeve but I get shorts without it and they wear out.