A flow battery can be thought of as a type of rechargeable fuel cell. The electrolyte fuel, in this case, is kept in large external tanks that can be pumped through a reactor. One of the characteristics of a flow battery is that the energy storage can be decoupled from the energy output. The size of the reactor determines how much power can be released at once, while the size of the storage tanks determines how much total power can be stored. This, in turn, makes it theoretically much easier to expand the size of a flow battery installation as compared to a lithium-ion battery. Doubling your battery life is theoretically as simple as doubling the size of the storage tank. Flow batteries can charge and discharge rapidly — refilling the tank with “charged” electrolyte can be as simple as opening a nozzle and pumping in the replacement fluid while the original electrolyte is recharged in a separate container.