Perhaps some day in the distant future, whenever you'd run out of battery all you have to do is slap on a fresh new snail.
That's right, scientists have invented the snail-based fuel cell:
By implanting enzyme-coated electrodes into a snail, researchers have turned the invertebrate into a tiny fuel cell. The enzyme coating one electrode triggers a chemical reaction that consumes glucose produced by the snail and generates electrons. A different enzyme coating the other electrode takes spare electrons and gives them to positive ions in the snail's hemolymph, the invertebrate equivalent of blood. Together, these reactions created a voltage difference between the electrodes of a little more than 0.53 volts, generating power of a few microwatts, the researchers report in Journal of the American Chemical Society.
No, it doesn't seem to hurt the snail:
The snail-based fuel cell—the first such implant to operate for an extended time without harming its host animal, the researchers claim—provided power for months, with power dropping when the glucose supply lagged and then surging again after the snail rested or ate.