NOVELTY - Electrochemical cell system comprises: at least one electrochemical cell, each comprising a fuel electrode comprising a metal fuel, and an oxidant electrode (430) spaced from the fuel electrode; a liquid ionically conductive medium for conducting ions between the fuel and oxidant electrodes to support electrochemical reactions at the fuel and oxidant electrodes; a housing configured to contain the ionically conductive medium in the electrochemical cells; and a gas permeable and liquid impermeable membrane positioned along a portion of the housing.    USE - Used as an electrochemical cell system.    ADVANTAGE - The electrochemical cell system: utilizes the gas permeable and liquid impermeable membrane that prevents permeation of the ionically conductive medium out of the electrochemical cell and permit the gaseous oxidant to permeate into the one or more oxidant electrode active materials; and does not adversely affect the flow of liquid electrolytes within the cell and/or the performance of the cell during operation.    DETAILED DESCRIPTION - Electrochemical cell system comprises: at least one electrochemical cell, each comprising a fuel electrode comprising a metal fuel, and an oxidant electrode (430) spaced from the fuel electrode; a liquid ionically conductive medium for conducting ions between the fuel and oxidant electrodes to support electrochemical reactions at the fuel and oxidant electrodes; a housing configured to contain the ionically conductive medium in the electrochemical cells; and a gas permeable and liquid impermeable membrane positioned along a portion of the housing and configured to close the portion of the housing to contain the ionically conductive medium in it but permit gas in the housing to permeate through it for venting of the gas (550) from the electrochemical cells, where the fuel electrode and the oxidant electrode are configured to, during discharge, oxidize the metal fuel at the fuel electrode and reduce an oxidant at the oxidant electrode to generate a discharge potential difference between them for application to a load. INDEPENDENT CLAIMS are also included for:    (1) assembling an electrochemical cell system, comprising: providing a cell module (100) configured to receive a liquid ionically conductive medium in it; installing a fuel electrode configured to store a metal fuel in it into a cell chamber (110) of the cell module; providing a plate for the cell module; installing an oxidant electrode and a gas permeable and liquid impermeable membrane on the plate; and joining the plate and the cell module so that the ionically conductive medium is prevented from permeating between them, and the oxidant electrode is spaced from the fuel electrode, where the gas permeable and liquid impermeable membrane are positioned along a portion of the cell module and configured to close the portion of the cell module to contain the ionically conductive medium in it but permit gas in the cell module to permeate through it for venting of the gas from the electrochemical cell system; and    (2) an oxidant electrode and vent assembly for an electrochemical cell, comprising the gas permeable and liquid impermeable membrane, and at least one oxidant electrode active material provided on a first portion of the gas permeable and liquid impermeable membrane, but not a second portion of the gas permeable and liquid impermeable membrane, where: when the oxidant electrode and vent assembly is mounted to an electrochemical cell comprising a fuel electrode and a liquid ionically conductive medium so that the liquid ionically conductive medium contacts the oxidant electrode active material and the fuel electrode, the fuel electrode and the oxidant electrode active materials are configured to, during discharge, oxidize the metal fuel at the fuel electrode and reduce a gaseous oxidant received through the gas-permeable and liquid impermeable membrane at the oxidant electrode active materials, to generate a discharge potential difference between them for application to a load; at least the first portion of the gas permeable and liquid impermeable membrane is configured to prevent permeation of the ionically conductive medium out of the electrochemical cell and permit the gaseous oxidant to permeate into the one or more oxidant electrode active materials; and at least the second portion of the gas permeable and liquid impermeable membrane is configured to permit gas in the electrochemical cell to permeate through it for venting of the gas from the electrochemical cell, and prevent permeation of the ionically conductive medium out of the electrochemical cell.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a cell assembly.    Cell module (100)    Cell chamber (110)    Air channels (350)    Oxidant electrode (430)    Gas vent (550)