Therm-ic's Sock Set V2 Uni 1200 pairs ski socks with heated batteries that you can control with your smartphone. If your feet feel a chill on the chairlift, just turn up the heat for extra heat. The batteries last for over fourteen hours, and they recharge via the included USB cable. The socks are longer than most ski socks to keep the batteries out of your boots, and the batteries are detachable for easy charging.