7V Battery Heated Vest Liner - Black - S/M Vest easily slips under your jacket and over a base layer or shirt for up to 8 hours of body-warming comfort, Microwire* heating system includes 3 built-in heating panels strategically placed on the chest and back to warm your body, Touch-button control technology, Includes 7V (2,600 mAh) rechargeable battery and single wall charger.