I just returned a Goal Zero nomad 7 to best buy today, it's too small couldn't charge anything, left it hooked to my old phone for 6 hours on a clear and sunny day, and it literally lost power.
I was thinking about trying the Goal zero nomad 15 because it's essentially double the size, if it doesn't work i'll return it as well....bad news is I still have 60 bucks on a gift card at best buy and i have NOTHING to get there.