This paper deals with the electrical double-layer capacitor's (EDLC) aging diagnosis for electric and hybrid vehicles. It has been shown in the literature that the aging of EDLCs is related to the constraints undergone by the component such as EDLC voltage (Vsc) combined with the operating temperature. The results of several studies show that the best indicators of the EDLCs aging are the capacitance and the equivalent series resistance. Some experimental methods allow the identification of these parameters but they are time consuming and cannot be embedded. This study presents a new method to estimate the EDLC parameters using least square algorithm based on data measurements of input/output of the system. In order to perform the aging test, a test bench is developed. EDLCs are aged at constant temperature and constant voltage. They are placed inside a climatic chamber at 70 °C and polarized at 2.9 V during the aging process. To quantify the EDLC aging, the equivalent series resistance and the equivalent capacitance are measured.