I know, the purists will want to slap me with my canoe paddle, but I do not like hiking or canoe tripping without my iPhone. Signals reach deep into the wilds now, and I like having the phone for GPS, emergencies, and writing. But keeping it charged is a challenge; there often isn't enough sun for a solar charger. Fortunately there are alternatives based on thermoelectric technology like the PowerPot and now, the very interesting Tegstove that just went up on Indiegogo.
Thermoelectric generators on the thermoelectric, or Seebeck effect, where "a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances. When heat is applied to one of the two conductors or semiconductors, heated electrons flow toward the cooler one." The greater the temperature difference, the greater the amount of energy produced. In my PowerPot, the cooler side is inside the pot, where the temperature cannot get above the boiling point of water.
This is where the Tegstove gets really interesting. It runs on standard butane cylinders; we have a backup emergency butane stove at our cabin that we use when the power goes out, that uses the same cylinder. When you use the stove, the phase change in the butane from liquid to gas absorbs a huge amount of heat and the cans get ice cold (actually, precisely ice cold-it's boiling point is 30°F). The Tegstove uses this cold as one end of the thermopile and the heat of the burning butane as the other to get a serious temperature difference between the two- enough to generate the power needed to charge its internal battery, which then charges the phone. This is a great feature; you don't need to be running the stove while you are charging but can do it at any convenient time, and not lose your phone in the dirt beside your stove.
The butane cylinders are a lot taller than the usual camp stove gas cans, so the design needs some form of stable base. They have designed a very clever folding tripod base that covers over a foot of width, which looks a lot better than my current stove where the actual gas can is the base.
The Seebeck effect was discovered in 1821; Boyle's law regulating gases under pressure in 1662. We had to wait until 2015 to see them combined so cleverly. What a great idea. More at Indiegogo and Tegology.