I'm getting about what I would get on a single CR123 3.7v in a SD... 3-4 hours (heavy vaper, here). Never had charging problems, my charger has a protection circuit in it. I've left it unattended many times, and don't rush to pull them out when it turns green. No special precautions.... charger is on my desk. Ok... so I don't leave it near the drapes. And I don't leave them in much longer than a day or so
This is the charger I use for them:
Ultrafire 3.6 volt or 3 volt RCR123 Lithium Battery Charger
I am going to append this comment to add that today, on only moderate use, they lasted 7.5 hours. This was 7.5 hours of constant moderate use... no down time. I guess I vape a bit less when I'm not sitting at the computer.