High voltage mods are available all over the internet now, The standard voltage is 3.7 and these mods are 5.0 and up. They use rechargeable, removable batteries that have excellent charge life. Basically you get more flavor, vapor and throat hit but the downside is they go through the liquid like crazy. Also you need to keep it wet as possible because when it starts to dry it will suddenly taste like an electrical fire. They are rather large and look like crackpipes. I currently own two of the HV mods and enjoy them both…
The XHALER from nhaler.com
This one is very easy to use, it puts out close to 6 volts and has a variety of colors to choose from. Its lightweight, Has a knob at the end of the shaft that adjusts the voltage as the battery fades, kind of a manual voltage regulator. The xhaler comes with a 901 and 801 adapter but you can purchase a 510 adapter for it. The batteries and charger are sold separately on the site for a good price. Overall I am very happy with it, If I had a complaint I guess it would be the button is set at the end of the shaft and gets a bit uncomfortable at times. Oh and the 901 adapter allows you to use the V4L cartomizers, and they preform well!