So in this guide I'll give you a bit of info on solar power and battery charging, as well as show you how to make a solar battery charger for all of $4.
If you'd like some solar panels or solar kits I have quite a few on my gadget site, browndoggadgets.com or you can also buy them off ebay or various other websites.
Step 1: What You Need
A clear, water-proof container. (Dollar Store tupperware with built in O-Ring)
AA Battery Holder (Radio Shack, also fits AAAs if you're careful)
One or Two Solar Panels rated 4 Volts or above
Blocking Diode (Radio Shack, or buy 100 for $1 off eBay.)
Tools you need
Time: 20-30 minutes