Hard to say without knowing how much you
vape.

A better indicator would be to test the voltage of the battery. Fresh out of a charger they're generally around 4.2v, and should be considered "dead" if much less than 3.7v. Most chargers will also refuse to start on an overly discharged battery as well. A good rule is "don't do this" as it will have some effect on the total battery lifetime, but it takes some experience to get a feel for when the battery is low without being "too low". It's not the end of the world if you run it dead, and usually if you let the battery sit for a few hours, it will rise somewhat and will charge again.
In theory a 3100 mAh battery has over 5 times the reserves of a 600mAh ego, which itself is somewhere around 2-4times the various 510 cig-a-likes, so depending on how long those were lasting you, the answer could well be 'yeah, they really do last that long!'
