Keep your feet warm and comfy with our extra thin heated sock liners that provide all day heat on a single charge. Made with a moisture-wicking micro polyester to keep your feet dry and spandex interlock fabric that forms to the foot for a great fit. Includes two small, at rechargeable VB320RC lithium batteries and dual charger. Each VB320RC 2000mAh battery weighs just around 2 ounces and discreetly tucks into a small storage pocket with hook and loop closure on the side of each sock. The battery comes with a built-in microprocessor controller with 3 power level settings. On the highest setting, the socks will provide over 3 hours of soothing warmth to the bottom of the foot, from the toes to your heel. Included with the socks is a battery strap in case you want the optional VB350 5000mAh battery that will provide 8 hours of heat on the highest setting and over 20+ hours on the lowest setting.