Sure, you can make solar-powered devices that store their excess energy in a battery, but what about the battery itself? Unfortunately, it's still behind the times -- the lithium-ion cells you see today have to be connected to another device to charge, and they're occasionally very dangerous thanks to their chemical makeup. A team of Indian researchers may have just licked those problems, though. They've developed a battery whose titanium nitrate anode (where current flows into the device) is driven by light, both natural and artificial. In a well-lit area, a prototype can recharge itself without using either an external source or unstable chemicals.