Thermacell 2.13

This foot warmer offers convenient remote operation, no wires or external batteries, and up to 2,500 hours of toasty heat to warm cold feet for about four winters of heavy use:

Rechargeable foot warmer is operated by a wireless remote control while the foot warmer is inside your shoes or boots
Uses high-tech wireless thermal technology—no wires, extension cords, Velcro® straps, or battery strap brackets, and no batteries mounted to the ankle, shoe, or waist
Powered by rechargeable, built-in lithium-ion polymer batteries embedded in the foot warmer insoles
Adjustable to three temperature settings to warm cold feet by remote control: no heat, medium (100 degrees Fahrenheit), and high (111 degrees Fahrenheit)
Can be recharged up to 500 times using the included charger. About $0.25 per use or $0.05 per hour of use.
It’s how to keep feet warm while hunting, working, or playing outdoors