Methodology for obtaining realistic supercapacitor (SC) Ragone from manufacturer datasheet only is presented in this letter, allowing to predict long-term wide-temperature SC power and energy performance for given terminal voltage limits. Analytical derivations are based on the simplified RC equivalent SC model, connected to a constant power element, taking into account manufacturer provided age and temperature parameter dependences. The main goal of the proposed approach is to allow practical energy engineer to quickly design a SC pack according to the desired long-term performance without performing further tests or requesting additional data. Simulation and experimental results are presented in order to validate the suggested methodology.