I haven't been vaping long enough, my 2 Triton 650mAh can vape as long now as they were out of the box some 5 weeks ago. But they won't last forever. You'll get less and less "puffs" per charge.
Lithium Ion batteries will last longer if they are not always taken to the "blinking LED" depleted stage. In other words, your batteries will last longer if you recharge them BEFORE they force you to.
For those of you with more advanced mods, this is a good reason to utilize a "puff counter". If you normally get 800 on a full charge, consider only going to 400. This advise is very useful for a mod like the MVP2 that doesn't have a replaceable battery.
Hey, kids, this is also true with iphones, laptops, any device that uses these Li-Ion batteries.