Provided is a highly reliable nickel-zinc battery which uses a separator having hydroxide ion conductivity but not permeability. This nickel-zinc battery is equipped with a separator exhibiting hydroxide ion conductivity but not permeability, wherein: the separator is provided in a sealed container so as to demarcate a positive electrode chamber for housing a positive electrode and a positive electrode-side electrolyte, and a negative electrode chamber for housing a negative electrode and a negative electrode-side electrolyte; the positive electrode chamber has a positive-electrode-side surplus space constituting a volume which allows at least some increase or decrease in a water amount according to a positive electrode reaction when charging or discharging; and the negative electrode chamber has a negative-electrode-side surplus space constituting a volume which allows at least some increase or decrease in a water amount according to a negative electrode reaction when charging or discharging. This battery is further equipped with a gas channel for connecting the positive-electrode-side surplus space and the negative-electrode-side surplus space to one another, and is configured so as to be capable of transmitting electrolyte and gas between the positive electrode chamber and the negative electrode chamber via the gas channel, according to quantitative changes caused by a charging or discharging reaction.