Biofuel cells use catalysts (chemical, enzymatic or microbial) to convert chemical energy from organic substrates into electrical energy. This paper investigates energy harvesting from several low-power biofuel cells to power a load under several volts. As biofuel cells can share the same fuel source, an isolation is required to aggregate energy towards high voltages (compared to a cell voltage). The proposed converter is based on the well known flyback topology. The efficiency of the flyback converter is about 60% for an input power of 10mW. The PCB area is 29 cm2 compared to around 74 cm2 for a previously built boost converter. The topology of the flyback converter includes a control circuit which allows a regulation of the input voltage to keep it around the maximum power point (MPP at around 0.3 V). This control circuit is powered internally through an auxiliary sub-circuit.