iPWR 1800mAh External Backup Battery charger for iPod, iPod Touch, Video, Nano, Classic, iPhone 2G, 3G, and iPhone 4, 3Gs With USB, Car, and Home-travel Charger - Work with i-Phone 4 Extends Music up to 40 hours, Extends Video up to 10 hours and Extends talk time up to 7 hours Streamlined, ultra-compact extends only 2.3" inches Rechargeable, can be recharged through Mini USB cable with computer or USB Car and Home charger Light-weight design Weighs a tiny 1.5 oz