The Airistech Vertex Twist cartridge battery packs a lot of features into its compact size.  The 400mAh battery gives you all day power and can easily be recharged with the included screw-on USB adapter.  There is a twist dial at the bottom of the battery that lets you adjust the voltage from 3.3V up to 4.8V.  If you have really thick oil, or prefer to use it at its lowest voltage level, you can press the button 2 times quickly to activate the 10 second preheat function.  The 510 threading allows you to attach any compatible cartridge on the market.

Airistech Vertex