In a flow battery according to one aspect of the present disclosure, a first liquid does not include an undesired compound. The flow battery satisfies requirement (i), (ii), (iii) or (iv). (i) An anode active material 14 includes graphite, and the first liquid has an equilibrium potential of not more than 0.15 V vs. Li/Li+. (ii) An anode active material includes aluminum, and the first liquid has an equilibrium potential of not more than 0.18 V vs. Li/Li+. (iii) An anode active material includes tin, and the first liquid has an equilibrium potential of not more than 0.25 V vs. Li/Li+. (iv) An anode active material includes silicon, and the first liquid has an equilibrium potential of not more than 0.25 V vs. Li/Li+.