Collecting electric power from the action of bacteria may prove a better solution than solar or wind power for far flung individuals and communities for low watt but highly critical needs.
In the video below one sort of MFC is explained. These are not batteries (to store power) but fuel cels (to generate power)
Lebone (pronounce the final e as a long A) recently announced that they have created an MFC (Microbial Fuel Cell) based in a bucket.
Hugo Van Vuuren, a 2010 TED Fellow founded Lebone Solutions "a social enterprise working in off-grid energy and lighting technology. We work to create global awareness for “Dirt Power” and end the energy and lighting crisis in Africa. We leverage our African roots and growing first-world experience to develop emerging technologies and models in a commercial and sustainable way."
A number of other researchers and aspiring manufacturers are working on the perfection of the biologically based electrical generators which initially would serve off the grid and impoverished communities with small but critical amounts of power.
A great source of information on Microbial Fuel Cells is MicrobialFuelCells.com
By the way Keegotech sells a Mudwatt battery for under $50 if you are inclined to experiment.
(SASL finder: Chris Lee)