Yocan B-smart is a compact and discreet vape pen battery, providing twist variable voltage from 2.0v to 4.0v. B-smart Features: 1. Fit Your Favorite 510 Cartridges 2. Customize Voltage Option(2.0V to 4.2V) 3. Compact And Portable 4. 320mAh Battery Capacity 5. Preheat Mode: Click the power button 2 times