Oh, I see, so only the gentlemen can help? what about the rogue badass dudes? or the ladies out there? Or those of us inbetweeners who refuse to decide which we are? Do we not get to help you? jk.
It is just like trying to determine how long a Bic lighter will actually last. The package says it will light 2000 times (at least, it used too). I have never actually counted, since I lose them all the time. Who knows how long it will last in weeks? Ya just never know. They may last a week, or a month, or a year. You simply don't get the desired effect anymore and must get a new one - usually at the moment you are least prepared for such a disaster. Bics are easy to come by, retailed everywhere. Ecigs require internet access, bank funds, shipping time - and occasionally delays. For this reason, we almost all say - MAKE SURE YOU HAVE SPARES, you can't just run down to the nearest store and buy one to get you through.