An improved quantification of electrochemical stability limits is proposed for electrolytes working in capacitors, where the enormous surface area of the electrode material renders the conventional determination of electrolyte decomposition inappropriate. Using the proposed new approach, reliable stability data are obtained for the description of non-aqueous electrolytes operating in double layer capacitors. With these new stability data it is also found that the electrolyte decomposition correlates with the surface concentration of the functional group rather than the total surface area of the electrode. This new method could be used to evaluate electrolyte:electrode interaction in more general systems in which the electrode has a high surface area without any irreversibility being desired.