It's a first MID-SIZE advanced device with VARIABLE VOLTAGE from 3.0-6.0 V, accurate to 0.1 V. With the Passthrough charging feature you are able to use the battery while it's charging. Moreover,the Li-polymer cell makes it the most safety V.V device in the market,no more worries when you enjoy the vaporing.We focus on the professional customers who are willing to experience the variable voltage but cost effective.