It is a portable compact lightweight durable and efficient solar charging and rechargeable battery storage device that can charge all USB chargeable devices such as smartphones tablets wireless speakers and more when electrical power is not available. Advanced power electronics enable faster charging and discharging of the rechargeable battery and faster charging of your external device when time is critical. Technical Specifications: Open-Circuit Voltage: 5.5-6V Converting Efficiency: 17-18% Solar Cell Area: 0.064 square meters USB Output: 4.5-5V 1.5A max 4000mAh Rechargeable Lithium Ion Battery Pack Operating temperature: -4°to 140°F (-20 to 60°C) Solar Power: 10W from 4 highly efficient mono crystalline solar panels