My Partner got me these as I come back from some Blood Bike runs in the middle of the night with very cold feet. USB charged before fitting in boots, and a 3 heat setting and off switch on key fob remote. Had to remove original insoles to fit into boots without being to tight, and you have to trim them to match your boot size. High heat 2 – 3 hours but longer on lower heat settings, a nice addition on those cold lonely trips when you cant feel your toes!!