The Hotronic Footwarmer S4 Custom Ski Boot Heater give your cold feet a boost of warmth to ski boots, snow boots, work boots or even tennis shoes. The battery packs provide almost an entire day’s worth of warmth. Use while you are skiing, snowboarding, bicycling, fishing and during any other cold temperature activity. Also available are the S4 Mounting Brackets for a quick attachment of the battery pack to ski or snowboard boots. These are the most powerful long-lasting Foot Warmer.