Whether you are skiing, snowboarding or hiking in winter: warm feet perform better. Although the charging time is extremely short the ultra-light lithium-ion batteries with 3 heat levels provide warmth for up to 29 hours. Suitable for use with all Thermic Soles & shoes with Therm-ic Inside (Trimfit sole covers for custom footbeds available) Ultralight lithium-ion batteries for quick charging & long life with minimal maintenance 3 heat levels, adjustable via included remote control & manual buttons on the battery packs Impulse Control stimulates blood circulation increasing foot comfort & reducing fatigue Global charger with charging display & country specific plug kit with an extremely short charging time As fitted to my ski test snow boots, these ensure that even when I am standing on cold snow for 8-9 hours per day filming & setting up, my feet stay super warm throughout, & my boots are also nicely warmed first thing in the morning before I put them on. As for ski boots, having skiied in Whistler at -32 Celcius I can vouch that these work, & make cold temperatures much more bearable. I am also diabetic, so I find the Impulse Control system very useful too, as it encourages good blood flow, important for those with diabetes where good circulation is critical!