The VV Box ranges from 2.8 to 7.2 volts. Hits like a truck with my 2ohm dual coil tank Carto at 4.3 volts, but I read somewhere that you shouldn't use dual coil at higher than 3.7. Doesn't taste burned or anything though. Quite impressed with this $13 kit. Though it's not for someone who isn't handy with a soldering iron. I used lead free solder as well and it was a pain to work with.