Since I got my Ego batteries last week, I have yet to see one run out. And I thought for sure I would today. My practice has been to stick the one I've been using on the charger when I get home from work, vape with the new one throughout the evening and next early morning, and head off to work with a fresh one. This morning I forgot to change batteries and got panicky until I realized I also had a fresh 510 and another fully charged 510 battery in the car charger. But I didn't need them anyway, and just vaped a bit on the 510 for a flavor change. Still haven't changed the Ego battery after >24 hours, and I'm an average-level vaper I guess, like 2-3 ML/day, and usually bottom out a 510 in an hour or so. And, I should add, I have an LR atty on it! I'm pretty amazed!