I got a 3.3-ounce, 5x6-inch solar panel for very cheap on Ebay before a few desert hiking trips last summer. It doesn't have an internal battery. This makes more sense to me because it's a lot less efficient to store and then transfer electricity than it is to pipe it directly into one device. The panel did a good job of keeping the phone topped off while hiking in the sun and using the GPS and map intermittently. When we stopped I was able to charge up a separate device by setting it in the sun (with the device in the shade underneath or a few feet away). On the second trip, however, the glue holding the connector on the back of the panel must have melted because it wandered off-center and it quit working. I plan to find a heat gun and try to fix it for my next summer trip, maybe with better glue. It's a good concept executed poorly: maybe someone makes something like it but better. I have to wonder if those 3x4-inch devices with the integrated batteries ever get enough solar energy to do much charging.