Flow batteries are electrochemical cells, same as regular batteries or fuel cells. Fuel cells run using fuel and atmospheric oxygen (though it can come from a

Flow batteries are electrochemical cells, same as regular batteries or fuel cells. Fuel cells run using fuel and atmospheric oxygen (though it can come from a tank in spacecraft). Normal batteries have all the electrolytes self-contained. Flow batteries use liquid electrolytes that pass through the battery. The big advantage of the flow battery is that you can refill the electrolyte tanks and go on your way.