NOVELTY - An apparatus comprises: at least one electrochemical flow cell (104), where the electrochemical flow cell contains anode electrode, cathode electrode and reaction zone between the anode and cathode; electrolyte storage reservoir configured to hold molten salt electrolyte and gas generated during charging of the electrochemical flow cell; at least one conduit configured to supply the molten salt electrolyte and the gas from the storage reservoir to the electrochemical flow cell; and at least one pump configured to pump the molten salt electrolyte from storage reservoir to reaction zone.    USE - As an apparatus (claimed), such as flow battery in the form of rechargeable battery.    ADVANTAGE - The apparatus includes high temperature metal-halogen flow batteries utilizing a non-aqueous (i.e. water free) molten salt electrolyte, thus allows the use of both zinc-chlorine (2.12V) and also the implementation of an aluminum-chlorine (3.02V) flow battery. The electrolyte containing the metal-halogen improves the conductivity of the apparatus such as battery. The operating temperatures i.e. greater than 100 degrees C of the flow cell allows enhanced electrolyte ionic conductivity, improved zinc or aluminum plating morphology and increased the reaction kinetics of the halogen electrode, thus provides improvements in higher overall energy efficiency for the flow battery.    DETAILED DESCRIPTION - An apparatus comprises: at least one electrochemical flow cell (104), where the electrochemical flow cell contains anode electrode, cathode electrode and reaction zone between the anode and the cathode; an electrolyte storage reservoir configured to hold a molten salt electrolyte and gas generated during charging of the electrochemical flow cell; at least one conduit configured to supply the molten salt electrolyte and the gas from the storage reservoir to the electrochemical flow cell; and at least one pump configured to pump the molten salt electrolyte from the storage reservoir to the reaction zone. The electrochemical flow cell comprises a stack of electrochemical flow cells located above or below the storage reservoir; where the storage reservoir contains a heater (126) which in use heats the electrolyte to at least 100 degrees C. An INDEPENDENT CLAIM is included for operating an electrochemical system, involving: pumping a molten salt electrolyte from a first portion of an electrolyte storage reservoir to a stack of electrochemical flow cells; and supplying a gas located in a second portion of the electrolyte storage reservoir above the first portion of the electrolyte storage reservoir to the stack of electrochemical flow cells.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic sectional view of the electrochemical stack above the molten salt/gas reservoir.    Flow battery stack (102)    Electrochemical flow cell (104)    Housing (105)    Electrolyte tank (106)    Gas space (118)    Heater (126)