The primary objective of all microbial fuel cell (MFC) research is currently to find ways to increase its efficiency by optimising design architecture and operating values. Microbial fuel cells (MFCs) are however very sensitive to changes in the configuration, source of inoculums and substrate initial pH values. This implies that power output results are hardly ever stable and there is need to find conditions which result in stable performance. A dual chambered batch MFC inoculated with small amount of untreated anaerobic digester sludge was initially operated at different external resistances of 120 O, 560 O and 1,000 O at a constant initial substrate pH of 7. After finding an external resistance that gives a high-power output, the MFC was operated using different substrate initial pH values of 6, 7, 8 and 9. Absorbance and voltage outputs were measured over a 5-d timespan and used to quantify the bacterial growth and electric output. High microbial activity was observed at pH 9, with electric output over a 1,000 O resistor, a voltage of 197.2 mV and power density of 10.3 mW·m-2. Power output inhibition was seen which was associated to membrane fouling. This study shows that microbial activities and methanogenic process can be controlled to stabilise maximum power output of the MFC by adjusting the initial substrate pH.