Abstract An undivided zinc–cerium redox flow battery was studied under a wide range of operational conditions, including: (i) electrolyte composition; the concentrations of ([Zn2+], [Ce3+] and [H+]), (ii) current density (0–80mAcm−2), (iii) electrolyte flow linear velocity (0.64–7.0cms−1) and (iv) temperature (20–60°C). The charge efficiency increased at higher current densities and at higher electrolyte flow velocities. Unlike the divided zinc–cerium system, the charge–discharge performance decreased at higher temperature, since oxygen evolution became increasingly favored at the positive electrode. The use of a low acid concentration led to a poor conversion of Ce(III) to Ce(IV) ions during the discharge cycle. Mixed electrolytes containing methanesulfonate and sulfate anions have been evaluated at a high Ce(III) ion concentration, e.g. 0.4moldm−3. After charging the battery for 4h, the conversion of Ce(III) to Ce(IV) ions became less efficient over time due to a greater fraction of the current being used in oxygen evolution. Critical aspects for improvements in the battery performance are considered.