Description The Hotronics S4+ Universal Boot Heaters provide a stronger and longer-lasting heating system that is easy to install and keeps your feet comfortable. The Battery inside the Hotronics S4+ Universal Heaters lasts up to 21 hours and the heater itself features 4 different heat settings.  Includes 2 battery packs Charger Heating elements Cambrelle Covers European Outlet 1 Pair of One Size Fits All - Heat Ready Insoles Heating Chart Hotronics S4+ Universal Boot Heaters