I can definately tell when my eGo battery is getting low on charge. It is a harder pull and alot let vapor. I usually have 2 going at the same time so I will try the other one just to compare. It usaully lasts an hour or so before it blinks at me after I notice the drop in production.
KayleePup
BTW-my eGo battery is the 650 and it will last me 10 - 12 hours depending on if I am also using my PT.