VOLT Battery Heated Slippers Nylon Rubber sole Includes two powerful 3.7v 2200mah rechargeable lithium batteries and a dual charger Comes with a wireless remote control for selecting power level setting. Small=W 5-7, Medium=W 7-8 or M 6-7, Large=W 9-10 or M 8-9, XL=W 11-12 or M 10-11, 2XL M 12