Abstract: The invention relates to a rechargeable battery system 1, comprising: at least one electrochemical cell 2 adapted for in charge mode to convert one or more gaseous electrochemical reaction reactant(s) 3 into one or more gaseous electrochemical reaction product(s) 4, at least one storage arrangement 5 for storing said gaseous electrochemical reaction reactants and products, wherein at least one of the gaseous electrochemical reaction product(s) 4 is converted to and stored as at least one chemical reaction product(s) 7,11, where said chemical reaction product(s) 7,11 has a lower gas pressure upon formation than the corresponding gaseous electrochemical reaction product(s) 4, a first fluid communication system 12 between the at least one cell and the at least one storage arrangement 5, wherein the first fluid communication system is configured to form a closed system within the battery system, whereby the battery system is adapted to generate an automatic gas flow between the at least one storage arrangement 5