Magnesium-sulfur batteries are currently researched for their potential as beyond Li-ion electrochemical energy storage devices. Despite the theoretical high volumetric energy capacity of magnesium metal anodes, sulfur is not very dense and many reports on magnesium-sulfur batteries use configurations with low active material loading and high carbon content at the cathode and high electrolyte content. Thus, the overall energy density of demonstrated magnesium-sulfur batteries is not very high. However, there may be potential for magnesium-sulfur batteries to be competitive in grid scale storage applications. In this presentation, we will report on our investigations related to magnesium polysulfide flow batteries as supported by an Amazon Catalyst at ECS award.