An economic design for an alkaline zinc-anode flow-assisted battery without membrane separators was tested at grid-scale of 25 kWh with a string of thirty 833 Wh cells in series, and also at bench scale with individual 28 Wh cells. The bench-scale tests allowed optimization of parameters such as electrolyte flow, choice of hardware material, electrolyte composition, and charge/discharge protocol. The best-performing bench scale cell cycled for over 3300 cycles with energy efficiency above 80%, and was selected as the design basis for scale-up to the 25 kWh battery string. Testing of the grid-scale string demonstrated 1000+ cycles with round trip energy efficiency above 80%. Two challenges observed at the bench scale were overcome for successful scale-up, namely a) passivation of the anode surface, which occurred when the anode experienced voltages 100 mV above zinc's rest voltage, and b) zinc particulates that jammed the gap between the electrodes and caused cathode degradation and passivation of the anode surface. Best practices to overcome these challenges and achieve long cycle life are presented.