Hi All I use an Eleaf iStick mini (10 Watts max) which only has variable voltage between 3-5 volts. You can’t alter or see watts. I combine this with an Aspire K2 tank. I’ve always vaped at 3.7 with an Aspire 1.8ohm general bvc coil because according to those charts online, anything above that is in the danger zone. However, on the coil pack it says to use 4.2-5 volts. What’s all that about?? Cheers!