Human Creations EnergyFlux Slim 4400mAh Rechargeable Double-Sided Hand Warmer/USB External Back Up Battery Pack Charger Warms on both sides of the unit, with two temperature settings (approx 109F and 120F) Charges via USB digital products including mobile phones, MP3 players, digital cameras, etc. Updated, UL-listed 4400mAh lithium-ion batteries with enhanced safety features can be used for over 500 recharges LED indicator display showing heat setting and remaining charge One-year warranty; contact TrueToSource or Human Creations any time for assistance. NOTE only EnergyFlux hand warmers sold by TrueToSource are genuine and eligible for Human Creations warranty and customer care