This variable voltage mod is for the extreme vapor. It uses two protected or high drain 18650 batteries, has the switching regulator for fantastic battery life, a mosfet on the regulator to limit current to the switch, and produces almost no heat off the regulator. There is no master on/off switch. Dial it down when putting in purse or pocket. Vapes for days not hours. Operates between 1 and 6.5 volts. Size is approximately 4X2X1 inch. This mod uses two 18650 3.7v LI batteries, not included. There is a 7 day wait on the Big Daddy Mod.