I have one battery that I used as my primary for about 2 months, and it's just starting to poop out on me. It charges fine, and lasts just as long as the others, but doesn't seem to be putting out the same voltage as my other batteries.
I would guess that it depends on how much of a vaper you are. It seems my smoking habits are hard to give up. I vape for about 10 minutes at a time and put it down for half an hour to an hour, which makes my batteries last a really long time. 4-5 hours usually.