The autonomy of the iPhone is a sensitive issue, especially since the machine is heavily used (3G, push notification, including GPS are greedy). We have seen many, many solutions with external iPhone batteries, or solar battery shells. Here's an accessory that may be of interest to backpackers on a spree. This is a backpack with solar collectors and a battery. The set is recharged by the sun and then used to recharge the iPhone. Inquiry, the battery capacity is 1000 mAh. In sunlight, it takes 4 hours to fully charge knowing that LED in the logo on the bag turns green when the panel is fully charged and red when it is under partial load. .