<p>Soluble lead acid flow batteries (SLFBs) are a promising single electrolyte energy storage technology in which Pb²⁺ ions are stored in solution and reversibly converted to Pb at the negative electrode and PbO₂ at the positive electrode. This membrane free configuration combines the low material cost of conventional lead acid batteries with the flexible architecture of flow batteries, offering potential for low cost and long duration energy storage. This review provides a systematic overview of SLFBs based on the Pb/Pb²⁺ and PbO₂/Pb²⁺ redox couples, with emphasis on electrodeposition and dissolution behavior, electrode electrolyte interfacial evolution, Pb²⁺ mass transport, electrolyte chemistry, electrode design, and scalable cell architectures. The main technical barriers to practical deployment are critically discussed, including Pb dendrite formation, incomplete Pb stripping, reduced conductivity and stability of the PbO₂ layer, concentration gradient induced polarization, and nonuniform reaction distribution under flow conditions. Recent progress in electrolyte formulation, additive regulation, electrode surface engineering, flow field design, and multiscale interface control is further summarized. By linking reaction mechanisms, interfacial structure, and cell performance, this review clarifies the key structure performance relationships governing SLFB operation and outlines practical strategies for developing reliable, recyclable, and economically viable long duration storage systems.</p>