Fuel cells hold the promise of never having to recharge a battery again, but until they actually become a viable alternative, we will have to continue plugging in our phones, PMPs, and laptops every night to charge.

Two researchers from the University of Wisconsin have come up with a way to recharge a battery without the need for a wall socket. Instead, you plug your device into your shoe and just start walking.

Electrical power harvesting from mechanical energy is not a new concept, and relies on reusing the energy generated from another process, in this case walking. The problem comes from how much energy can be converted using this syetms using existing methods which have only produced minimal power levels until now. However, the research pair’s system is capable of generating up to watts rather than the more typical milliwatts of power–enough for a decent charge.

The system reverses the process of electrowetting and uses a new microfluidic device that forces conductive liquid microdroplets through a nanostructured substrate. In its simplest terms, the movement of this liquid through the system creates a flow of electricity ready to be harnessed by whatever you plug in.

The idea has led to the creation of a company named Instep Nanopwer which is trying to commercialize the tech in a number of different devices. For the walking system it takes the form of three connected parts that are embedded within the sole of a shoe. The problem they have yet to overcome is the best way to connect a device to that shoe as a trailing cable is just asking for trouble.

While it may not solve the issue of always having a full battery, it certainly makes a lot of sense to reuse the energy from walking to at least partially recharge a battery. For those who commute to work on foot, or regularly go for walks or runs as exercise, it could mean a reduced power bill at least. The other good news is there is no extra energy required to walk while wearing the shoes harvesting the energy, so it really is a free power source you could work into your daily exercise and activity.