Batteries of various technologies and form factors get a lot of attention for many reasons. Everyone is looking for a battery with higher energy density by weight and volume, with superior discharge (and even charge) specifications, and low cost. As a result, there's been lots of attention on lithium-ion (Li-ion) chemistry and its many variations, since that seems to offer – at least for the foreseeable future – the greatest potential (pun intended) in meeting those density objectives.

Still, there are applications where unusual chemistries, construction, and form factor are the priorities, more than just an incrementally better Li-ion cell. Consider the work being done by a team lead by Prof. Christopher Bettinger at Carnegie Mellon University. They are developing edible, biocompatible batteries that use non-toxic materials already present in the body, with available liquids such as stomach acid as the electrolyte; see references below (Figure 1). His team has produced cathodes based on melanin, a pigment already in the body, and anodes made of manganese oxide, which is also already present; other versions based on body-friendly materials have also been developed.

The idea is that the electrodes will dissolve harmlessly after use. Most of the resulting batteries, using a variety of soluble cations, had modest voltages (between 0.5 and 0.7 volts); although definitive specifications are hard to find, there was one mention of 5 milliwatts of power for up to 20 hours.