Notice how battery chargers get smaller & smaller. It's becasue everything is a chip now. I bet we couid make solar rechargables with present tech. Imagine a big D-Cell with a solar panel on the outside jacket so that when you place it in a sunny window, it charges itself in 3-5 hours. It would be perfect fpr camping too. You can include a chip to that regualtes the charge & use multiple power sources & types, it regualtes it's own charging, you jsut have to hook it up to a power source to rapid charge or leave it in the sun to trickle charge for free. 