An electrochemical cell system is configured to utilize an ionically conductive liquid flowing through a plurality of electrochemical cells. One or more hydrophilic filters for venting of gas from the cells are provided along a flow path for the ionically conductive liquid, so as to permit gasses that evolve in the ionically conductive liquid during charging or discharging to vent outside the cell system, while constraining the ionically conductive liquid within the flow path of the electrochemical cell system.