The use of large capacitance supercapacitors in series or series/parallel configurations has been envisaged and evaluated as a basis for load-levelling, and hence performance enhancement, in electric vehicles (EV) powered primarily by rechargeable batteries or fuel-cells. In this paper, charge/discharge efficiency in duty-cycles of the supercapacitor component are examined in relation to distributed resistance in porous double-layer and redox-type devices which restricts efficiency of discharge and recharge cycling, especially at high rates. Results of quantitative experiments on the responses of a five-element RC model hardware equivalent-circuit and a gold brush electrode an presented. Potential-recovery after discharge and potential-decay after recharge, and potential changes following load variations, enable efficiencies of charge delivery and acceptance to be evaluated.