It's not difficult to implant an electronic device into an animal, but whatever you put in will be limited by the battery you include. A growing number of scientists, however, are working on batteries that can be powered by the animal's natural metabolic processes. In one of the first successful examples, a team from Clarkson University and Ben-Gurion University of the Negev has implanted a biofuel cell into a living snail, generating electricity from the glucose in its bloodstream. When the cell's electrodes are hooked up to an external circuit, it can produce between 7.45 and 0.16 microwatts of power. For comparison, a watch battery puts out around one microwatt. The research was led by Professor Evgeny Katz and published in Journal of the American Chemical Society.

In the past few months, researchers at other universities have successfully implanted biofuel cells in insects. The lifespan of these creatures, however, limited their time as batteries to a couple of weeks, while the snail was able to produce steady power for several months. Unfortunately, its electricity production dropped off by about 80 percent after 45 minutes, meaning that the researchers will either need to find a way to generate more power or to store it for extremely economical future use.

This research has obvious application for biological research or surveillance, since an animal-powered battery could allow for tracking or information-collecting devices to last much longer without including a bulky battery. It's also possible that we could eventually use this power for implanted medical devices in humans, although generators that use body heat or kinetic power are likely more practical in the short term. Katz, for his part, says he plans to try the fuel cells in larger animals like lobsters.