Abstract: An electrolyte system suitable for a molten salt electrolyte high temperature battery is described consisting only of a first component which consists of one or more lithium halides and a second component which consists of one or more lithium compounds which are not lithium halides, and is preferably one or more of lithium sulphate, lithium sulphide, lithium metaborate and lithium oxide. A molten salt electrolyte high temperature battery is described incorporating the electrolyte (2), an anode, preferably of lithium or a lithium alloy (3), and a cathode, preferably of iron disulphide (1).