Do you care about length? Have you tried the 510 mega
batteries?
Also, what filler do you use? I set up my cart with the PTB Made Easy (takes minutes to set up) and that improves the flavor a LOT and reduces how often you have to top off. I refill with 8-9 drops every time, unlike with polyfil, where you get to the point where it only take 2-3 drops and you're constantly topping off. The PTB Made Easy
mod also is really easy to rinse out and reuse - takes seconds to do. You just rinse it out if it's taking less on refills or if the flavor seems diminished. If I was still using polyfil or some complicated cart mod, I'd probably want to chuck my 510, too! LOL