In review examineі base properties of modern non-aqueous electrolytes for li-ion batteries and hybrid supercapacities taking part in the formation of power density, electrochemical and thermal stability. Discussed such aspects as the electrolytes functions in electrochemical power sources, physicochemical and electrochemical properties of electrolytes for supercapacitors, the physicochemical and electrochemical properties of electrolytes for primary and secondary batteries, and methods of electrolytes research. As the base methodі for electrolytes studies considered: electrochemical impedance spectroscopy, voltammetry, amperometry, viscosimetry, and combined Ramman spectroscopy.