HOW TO USE: Power Up – Charge the provided ActionHeat 5-Volt batteries. Plug-In – Connect the batteries to the USB cords located in the pocket on the side of the boot. Turn On – Press and hold the touch-button control on the sock for 3 seconds. Press the button to cycle through the heat settings DESIGN: Powered by rechargeable 5V batteries and can last up to 5 hours Three heat level settings Weather-resistant Turn off LED ghost-mode MAXIMUM HEATING TIMES: High: 140°F - 2+ Hours Medium: 120°F - 3+ Hours Low (Blue): 100°F - 5+ Hours