While some people like the simplicity of an auto-draw vape, those who want ultimate control over the vaporization of their concentrates should go with an option that allows you to change voltage. The Variable Voltage Battery with Charger can connect to any 510 thread cartridge. The 350mAh battery has a single button that helps you turn the battery on and off (press 5 times), adjust voltage (3 times for each), and activates preheat (2 times). There are three different voltage levels; green - 2.8v, blue - 3.4v, and red - 4.0v. Switch between them as you like! Use the lightest setting for a tasty smooth hit then switch it to red for a more robust flavor. The included USB charger fits the threaded side perfectly for easy charging (red for charging, green for ready). The Variable Voltage Battery with Charger is designed and developed in the USA.