The following link is to a BBC News Online article about how certain microbes can consume almost anything, and their “waste” output is electricity.  Of course, if there will ever be a battery made using this technology, it is not going to happen within the next 5 years.  Still, it’s something to think about.

http://www.bbc.com/earth/story/20160613-there-are-microbes-that-eat-and-poo-nothing-but-electricity