Abstract: An electrolyte for use in a capacitor or a battery comprising a solution of (a) at least one salt selected from the group consisting of alkali metal salts, transiton metal salts, ammonium and ammonium derivatives salts, zinc salts, cadmium salts, mercury salts, lead salts, bismuth salts and thallium salts of (b) at least one acid selected from the group consisting of monobasic, dibasic and tribasic acids (c) in an aprotic solvent substantially free of protic impurities. The acid may be selected from the group consisting of perchloric acid, tetraflouboric acid, thiocyanic acid, trifluoromethanesulphonic acid and haloid acids. The salts may be selected from the group consisting of partial esters of at least one of boric, sulphuric and phosphoric acid reacted with compounds containing an alcohol group or may be an alkali metal tetrafluroborate. The capacitor is stable and has improved linearity, working voltage, capacitance per unit area, shelf life size, leakage current, and internal series resistance.