Abstract: A bio-battery includes a biomolecular energy source, a first electrode and a second electrode. In some configurations, a bio-battery may also include a first cell containing the first electrode and the biomolecular energy source, and a second cell having a reducible substrate and the second electrode. The first cell can be in ionic communication with the second cell, for example by a proton exchange membrane. Various biomolecular energy sources can be used, including proton donor molecules or electrolytically oxidizable molecules. For example, the biomolecular energy source can be selected from the group consisting of Nicotinamide Adenine Dinucleotide (NADH), Nicotinamide Adenine Dinucleotide Phosphate (NADPH) and 5,10-Methylenetetrahydrofolate Reductase (FADH).