The increasing demands for grid peak-shaving/load-leveling and renewable energy integration lead to fast development of electric energy storage techniques. A novel redox zinc-nickel flow battery system with single flow channel has been proposed recently. This single flow zinc-nickel battery system provides a cost-effective solution for grid energy storage because not only does it possess high efficiency and long life cycle, it also has no requirement for the expensive ion exchange membranes. In this paper, the basic characteristics including its principle and current research progress are introduced. And based on the electrical characteristics of the battery, an equivalent circuit battery model is proposed. Experimental validations show that the model provides a good indication of battery performance under both steady and dynamic conditions. The steady state output of the scaled-up 200Ah battery is also estimated by the model and compared with experiment results. At last, the possible improvement in the battery for future applications is discussed.