The purpose of this graduate work was to prepare a carbon electrode along with its electroactive material and to put together a double-layer supercapacitor and to analyze its characteristics with cyclic voltammetry. Then analysis was also done on a commercial supercapacitor (Eaton PowerStor® HB Series HB0830-2R5605-R) according to the given standard HRN EN 62576 and additionaly using the electrochemical impedance spectroscopy (EIS) method. The prepared electrode material was prepared as a paste consisting of the activated carbon Norit® DLC Super 30, conductive carbon black Timcal® Super C45, poly(vinylidenefluoride) (PVDF) and organic solvent N-methyl-2-pyrrolidone (NMP). The paste was put on the Al working electrode. Four electrolyte solutions were made; two of them with polar aprotic organic solvents ethylene carbonate (EC) and propylene carbonate (PC) with composition 50:50 by volume. One solution used LiPF6 as the electrolyte while in the second one the electrolyte was LiBF4 both with molar concentration of 0,1 mol dm^-3 and the other two solutions have been made out of same solvents which have not been mixed up together and the same electrolytes with the same concentrations. A supercapacitor was constructed in a vessel reactor and its characteristics have been analyzed with cyclic voltammetry in different potential ranges. After that characteristics of commercial supercapacitor were measured according to the standard for testing the electrical double-layer capacitors for use in hybrid electric vehicles HRN EN 62576. As a result of testings, three groups of dana were obtained: 1. capacity, internal resistance and maximum power density, 2. voltage maintenance characteristics, 3. energy efficiency. Additionaly testings were carried out using the electrochemical impedance spectroscopy (EIS) resulting in Nyquist and Bode plots from which ohmic resistances, capacities and inductivities were calculated. All testings of commercial supercapacitor were done at three different temperatures; 0°C, 25°C, 60°C.