Provided is a highly reliable nickel-zinc battery including a separator exhibiting hydroxide ion conductivity and water impermeability. The separator is disposed in a hermetic container to separate a positive-electrode chamber accommodating a positive electrode and a positive-electrode electrolyte from a negative-electrode chamber accommodating a negative electrode and a negative-electrode electrolyte. The positive-electrode chamber has an extra positive-electrode space having a volume that meets a variation in amount of water in association with reaction at the positive electrode during charge and discharge of the battery, and the negative-electrode chamber has an extra negative-electrode space having a volume meeting a variation in amount of water in association with reaction at the negative electrode during charge and discharge of the battery. The nickel-zinc battery further includes a gas flow channel that connects the extra positive-electrode space to the extra negative-electrode space such that the spaces are in gas communication with each other.