The Hotronic Foot Warmer S4+ Universal Ski Boot Heater warms your feet, no matter what footwear you are wearing, in any weather. Newly redesigned with a raised protector on the switch to prevent unexpected switching. This super powerful set up keeps your feet warm in the coldest weather with its S4+ battery packs. The heating elements have 4 settings; 3 for maintenance and 1 for an extra blast of heat when it is so cold you have to jumpstart your reindeer. The battery recharger works with Hotronic S, e and m battery series, and is compatible with American, European and Canadian outlets. The powerful S4+ battery is powered by NiMH AA cells, for perfect operation even in the coldest temperatures when you need them the most.