Variable Voltage or EGO type 510 batteries were the first alternatives to original e-cigarettes and the first to allow the use of tanks or clearomizers as they were then called. The variable voltage came from the ability to set a range of volts for use, usually by spinning a dial on the bottom of the device or with more modern devices 3 clicks on the device fire button.
As sub ohm gear started to become popular these low power devices fell out of favor but with the advent of salt nics, thick oils and other “vape juices” the 510 variable voltage battery has made a major come back.
In deciding which 510 battery device is best for you various factors should be considered such as the range of voltages, ease of adjustments and for thicker materials preheat is a must have.
For thinner oils setting under 3V may be desirable where thicker substances may require 4v or higher. Preheat usually starts out at a very low voltage and then increases slowly up to the range of your settings for a full and flavorful hit from your cart.