Here is a smartphone charger that lets you use a fire to recharge your battery. The JikoPower Spark is a thermoelectric charger. It can charge your phone, speaker, and other small gadgets in a few hours. The difference between the hot and cold side of the module determines the electrical output. Just add water to the top module, and you are ready to go.
This smartphone charger can be useful for camping and emergencies. More info is available here.