The invention provides for a method of discharging a chemical source of electric energy in two stages. The chemical source of electric energy comprises a positive electrode (cathode) including sulphur or sulphur-based organic compounds, sulphur-based polymeric compounds or sulphur-based inorganic compounds as a depolarizer, a negative electrode (anode) made of metallic lithium or lithium-containing alloys, and an electrolyte comprising a solution of at least one salt in at least one aprotic solvent. The method comprises the steps of configuring the chemical source of electric energy to generate soluble polysulphides in the electrolyte during a first stage of a two stage discharge process, and selecting the quantity of sulphur in the depolariser and the volume of electrolyte in a way that after the first stage discharge of the cathode, the concentration of the soluble polysulphides in the electrolyte is at least seventy percent (70%) of a saturation concentration of the polysulphides in the electrolyte.