Just curious, for those of you who carry thier phones on longer treks, have any of you used one of the little solar gadgets that claim to charge your phone, or can be plugged into your phone like a fresh battery?

Do these things really work? Have you used them in the field for...say...a 3 - 5 day trip...or longer? I'm a little skeptical, but thought someone here might know...

Thanks ahead,

J.