Suitable for use with all ThermicSoles and boots with ThermicInside * Ultralight lithium-ion batteries providing warmth for up to 18 hours: 1: 37°C / 99°F 13 - 18h 2: 45°C / 113°F 6 - 8h 3: 70°C / 158°F 2.5 - 3.5h * The 3 heat levels can be set at the push of a button: 1: 37°C / 99°F 2: 45°C / 113°F 3: 70°C / 158°F * The Impulse Control stimulates the blood circulation * Standard charger (EU/US/UK) with automatic charging function, Extremely short charging time (2-3h)