The Goal Zero 21005 Guide 10 is a device that can be charged by a USB port. what is charged in the device are 4 aa batteries. then you hook up your phone and can power your phone. however, if you don't have access to a USB port, you can just insert fresh AA batteries and use your phone. they also sell a device (Goal Nomad Solar Panel) which can clip to your backpack. while you hike it pulls solar energy into the batteries and then you could use it to run your phone. Both devices are available on Amazon if you want to look at technical details. I am just wondering if this is the best, lightest device to accomplish this.