Another item I received from my wishlist for Christmas was a Scosche SolBAT II Solar Powered Backup Battery and Charger. The device recharges slowly via solar power or can be rapidly recharged via USB. It functions great as a backup battery for USB powered devices.
Not long after I received it I had a chance to test it out by recharging my iPhone on a camping trip where outlets were rare. It managed to recharge the phone (down to at least 75%) up to 97%. The manual states that recharging the battery from a complete discharge via solar power requires 4-5 days, but according to the LED indicators it managed to recharge somewhere between 50%-75% in one day.
It’s not capable of keeping my phone fully charged over several days but it is well suited to adding some power in situations (or emergencies) where I don’t have access to an outlet.
Updated 06/22/2011: I haven’t used the charger much since my last trip. Since then it’s been sitting in a window. About a week ago I decided to charge my iPhone to run the solar battery through a cycle. It helped top off the phone but it didn’t recharge as much as when I first used it. After letting it recharge for more than a day it showed it was about 3/4 charged, though it wasn’t in direct sunlight. Regardless, it still seems to be a good charger. I saw one on clearance somewhere for about $12 and should have bought it. The next time I see one on sale I’ll purchase one or two more.