Brian, A couple of years ago we were at Isle Royal NP in Lake Superior and there were a bunch of young guys camping there. One of them had a solar charger and he was using it to make calls on his cell phone. Seems he had run his battery down and he made a few calls with just the solar charger. As we were all headed to the mainland he planned on charging his phone there, He did say he had used it to fully charge his phone but it took a long time. I believe it was from Sharper Image, pretty small and foldable. So while I haven't used one this kid had and liked it.