An experimental study on hydrogen and oxygen evolution was carried out in a sealed zinc–nickel oxide battery. The effects of flowing electrolyte on gas evolution were quantitatively evaluated. The results show that both the hydrogen and oxygen evolution are suppressed by making the electrolyte flow on a regular cycle. This is due to increased cell polarization in the non-flowing case attributed to the concentration boundary layer of zinc (zincate) ion near the anode surfaces. Though the Coulombic efficiency in the flowing case was higher than that in the non-flowing case, the fraction of gas evolution against Coulombic loss was the same for both the cases. When deeply discharging the cell, more hydrogen is evolved in the flowing case than in the non-flowing case.