I have been using these heated sock for these extreme cold mornings and keeps me smile... I can control heat strength by iphone .. The battery last about 7 to 8 hours depend on heat level and my toe never felt cold. We can wash these socks in wash machine without issue (just do not put in dryer) The only issue i had is ihone does not work in cold temp so need to warm it up. The heat level is also be controled by manual button on the battery as well so i phone is not really needed but nice to have. These socks are thin enough to use for Race boots and also FIS legal... Unfortunately they are little pricy at $299 First Inline Sports in Kingfield is a dealer ... Santa did well for me this time
http://www.lenzproducts.com/heat-dry-hy ... socks.html