Portable solar chargers have made it easy to replenish mobile devices off-the-grid – place the solar panel under sunlight, plug in your phone/flashlight/GPS, and wait for the power to trickle in. If there’s any downside to solar charging, it’s that the whole thing just takes so darn slow. If there is running water anywhere in the vicinity, you might want to bag up the solar charger and use the Blue Freedom instead.

A portable hydroelectric power plant, it lets you replenish mobile devices by harnessing the energy potential in streams and rivers. Considerably faster than solar charging, it’s supposed to be capable of charging an iPhone 6 in as little as one to two hours, depending on the rate of water flow and how consistently it runs.