Battery inner pocket design, working with a common 5V/2.1A or above power bank with a USB port (Power bank not included). Built-in with 9 carbon fiber heat elements, with a 2 switch design–Back & Belly switches can be operated separately to create constant heat for core body zones. Carbon fibre heating wire, heating up in 10 seconds, overheating protection, lightweight, flexible and safe. With 3 heating levels, supply continuous heating time 10-12 hours for low 86?, 8-10 hours for medium 104?, 6-8 hours for high 122?. Multiple size unisex heated vest can be wore under jacket or as outwear. It fits all kinds of outdoor winter activities, like ice fishing, hunting, skiing and hiking. Hand and Machine washable.