The resistor in the switch holds the Prodigy to 5v. The
batteries that come standard are 2 @ 3.0v. If you had no resistor then it would be a 6v device. You can get a switch without the resistor that will allow you to do this. That switch without resistor is also good for using the single huge battery at 3.7v.
So if you have the standard unit you are running at 5v.
I wish PureSmoker would offer a kit to convert the Prodigy to 3.7v. Maybe a kit that had two big
batteries, a charger for them, and the switch without resistor. As it is now you would have to spend 26.95 (Switch) + 7.99ea (18650 3.7v 2200mAh battery) +14.99 (charger) = 57.92 to convert plus two batteries. Maybe a 45.95 deal or something like that would be nice. Hint, Hint.... lol...