The optimum operating parameters for dielectric elastomer generator (DEG) systems, in the sense of the global optimum, refer to their maximum performance in terms of elastomer tensile strength, breakdown voltage value etc. In practice, operating a DEG close to the limit of its strength will involve a limitation of its durability, as DEGs can also suffer fatigue damage. Deviation from the optimum operating parameters, either for reasons of increasing their durability and reliability or simply because of practical limitations in a given application, makes it necessary to search for local optimum operating points. The aim of this study was to analytically determine the optimum working point of a DEG generator operating in a rectangular cycle (constant charge, constant voltage) by the value of the voltage difference between the upper and lower sources. On the basis of capacitance measurements on two generators with two and three active layers (electrodes) operating under uniaxial tensile loading, the theoretical values of the optimal voltage difference ΔU were calculated. The results were then verified experimentally. The empirical values were found to be in agreement with the theory (Fig. 10) and showed that it is possible to predict the performance of a DEG accurately by knowing the variations in its electrical capacitance.