Here is a post that shows different batteries being tested and actual voltages going to the atomizers. In many cases, you are not really vaping at 3.7v.
http://www.e-cigarette-forum.com/forum/joye-510/65055-battery-voltages-surprise.html
This may be helpful when choosing what model of pv to purchase.
http://www.e-cigarette-forum.com/forum/joye-510/65055-battery-voltages-surprise.html
This may be helpful when choosing what model of pv to purchase.