Hi, I don't know so much about electronics but... I know when you have a junction of two metals that is heated you can get a small voltage. Like wrapping a piece of wire around a nail and holding a flame over it produces a very small but measurable voltage. This is a thermocouple as far as I know. Now I've heard different metals can produce larger voltages. I was wondering if it might be possible then to make something that could use heat to charge a small battery. It would only have to be enough to light a single LED for 4-5 hours. So, you could put the junction in some charcoal that is burning all day (like charcoal ovens in 3rd world countries), and then come nighttime have a battery that has enough charge to make a light for you. I don't really know how a battery charger works, I'm just wondering if something like this is possible. Thanks.