Stay warm on the trail and keep your portable electronic devices fully charged with the National Park Foundation Rechargeable Power Pack & Hand Warmer. Features: Two-in-one device: portable USB power pack and hand warmer with special edition National Park Foundation design, 4400 mAh rechargeable battery provides six hours of continuous heat, Charges smartphones, MP3 players and many other USB-powered devices, Ergonomically designed to fit easily in your pocket or bag, Silicone caps make unit durable and weather resistant, Heats up quickly and reaches a maximum of 113 deg, Rugged aluminum housing.