Good trekking accessories

I ordered the 14W solar charger, since mine is on multi-day trekking tours often run out of juice for's smartphone / tablet. Just when you want to navigate / photograph with mobile devices, the battery is quickly running out. The solar charger offered here has two USB ports, so two devices can be loaded simultaneously. This, however, doubles the charging time, what should be clear. The individual solar panels are rigid and can not bend. It is sewn a pocket in which a smartphone has space.

Charging time test results:
individually charged in full sunlight (noon), all apps have been completed and the flight mode is active (no network activities!):
iPhone 3GS: 28% per hour
iPad 3: 20% per hour

On the iPhone 3GS, I noticed that even loads with a few clouds. However, Apple devices have the flaw that they cancel if there is insufficient charging current, the charging process with an error message and unfortunately do not start automatically if there is sufficient sunshine again. Since the plug must be plugged again. I do not know how that behaves with non-Apple devices.

edit [24/05/2015]: The iPhone 4s there is no interruption in case of insufficient charging voltage longer. Advantage: The Smartphone can remain plugged into the solar charger and loads depending on the lighting conditions sometimes more, sometimes less. Disadvantage: For very heavy cloud cover is removed from the smartphone battery because the reverse current energy storage. This phenomenon occurred in my 4s but only on, when the sky was overcast with dark gray rain clouds. In dry, cloudy weather, the solar charger recharges my 4s on anyway. Therefore, it does not require direct sunlight.