PowerSocks combine proven Therm-ic technologies with the high-tech materials and patented functions of X-Socks. Integrated heating elements under the toe area provide heat for up to 16 hours. A rechargeable battery sits neatly at the top of the sock with an imperceptible heating element attached outside. Bluetooth technology means the devices can be controlled or programmed from your smartphone. This optimised design and the anatomic shape ensure an ideal fit of the sock and continuously warm feet when participating in outdoor winter activities. Set includes the Therm-ic S-Pack 1400 B battery, a pair of anatomically designed high-tech socks and USB charging cable (wall plug not included).Power Source: S-Pack 1400B