Brass Knuckles Variable Voltage Battery Brass Knuckles battery offers a vape pen that is the perfect size and power for your oil cartridges. Vape in style with this sleek and convenient battery that has adjustable voltages. This allows the user to vape their cartridges in 3 different heat settings, along with an optional preheat function. The battery is available in different color options to match your fly. Features: 510 Thread Battery Capacity: 900mAh Turn On/Off: Press the button 5 times quickly. Adjust Voltage: Press the button 3 times quickly. Variable Voltage: Green - 2.4V, Blue - 3.2V, Red - 4.0V Preheat Function (2.0V): Press the button 2 times quickly.