Here's the one I have...

[Link: rei.com]

I chose this one because of the corner hooks. The holes are large enough for the buckle of my Gregory pack to fit through, so it sits right on the back of the pack without any "duct tape and bubble gum"...

Charges a Samsung Galaxy S4 fully twice. The battery in the charger itself charges fully in one day's hike.

If you don't need the extra weight and size of the solar part, the battery pack is removable and functions as a standalone portable charger.

Love it.