IMP500-3500 Solar Powered External Backup Battery For iPhone 3G 3GS Blackberry Android etc. High solar energy converts efficiency: Monocrystalline silicon/polycrystalline silicon, over than 17% (Max) High capacity built-in polymer li-on battery: 3500mAh/3.7V (12.95Wh) Protect function: short circuit, over-current, over-charging, and over-discharging Portable and Eco-Friendly as It can be charged directly with Sun-light as well as USB port and AC adapter Eco-friendly, Solar light can be your last resort if you need to power your mobile devices