So, first of all, why bother? Well, solar-powered chargers may work fine in direct sunlight, but can be thwarted by heavy clouds, tree shadows, or even just high latitudes. They also don't do a whole lot at night. Thermoelectric chargers, on the other hand, require you to build and maintain a fire.

 

The HydroBee ... well, yes, it requires you to be close to a stream or river. If you are, though, it will work in even a weak current, regardless of the weather or time of day.