Step potential electrochemical spectroscopy (SPECS) has been developed as an electrochemical method for application to electrochemical capacitors, in this case for an activated carbon electrode in 0.5M H2SO4. The method involves the application of a sequence of small potential steps over the potential window used by the electrode under study, followed by a relatively long rest time after each potential step. Modelling of the SPECS data has been used to extract the contributions made by electrical double layer charge storage and diffusional (redox) processes to the total electrode performance. Outcomes from the application of this approach highlight the dominant charge storage mechanisms at both high and low cycle rates, as well as allow differentiation of ‘capacitor-like’ or ‘battery-like’ electrode behaviour. The SPECS data has also been analysed so as to enable calculation of voltammograms at different scan rates for the electrode system. Finally, electrode performance data has also been presented and discussed.