The yeast-based fuel cell produces around 40 nanowatts of power, compared to the microwatt a typical wristwatch battery might produce, Chaio says. That might be enough power for some devices if it were coupled with a capacitor to allow energy to be stored. The yeast could also be genetically engineered to boost its power output.
Yesterday researchers at the University of British Colombia in Vancouver announced that they'd created a tiny battery (pictured) that could draw power from human blood. They're basically cyborg batteries, half biological and half technological.

The batteries are designed for use in pacemakers and other implantable medical devices. A small colony of yeast lives inside each battery, and this living core of the fuel cell can draw energy from glucose (sugar) in blood flowing around it.

Now that we can have bio-batteries implanted in our bodies, we're well on the road to becoming cyborgs. We can become biological organisms implanted with technology that is in turn implanted with biological organisms.