Battery warmed socks

For a friend of a friend...
This is a little weird.
Does any one know where battery warmed socks can be purchased?
Note: He wants the batteries to be located above his waist line for easy
access while in his waders.
I told my friend to tell his friend to solder a couple of leads onto the
battery terminals and run them up his waders for easy access. He said he
already told him that, but he would rather the batteries were already remote
from the socks.
Any help will be sent along.
Guy