Redox flow batteries are promising candidates to facilitate the integration of renewable sources into the energy mix. This is associated to their durability, efficiency and fast response. However, deployment of existing redox flow batteries is hindered by the relatively high cost of the (typically vanadium-based) electrolyte. Manganese is an abundant and inexpensive element that is widely used in disposable alkaline batteries. However, it has hitherto been little explored for redox flow batteries due to the instability of Mn(III) leading to precipitation of MnO₂ via a disproportionation reaction. By combining the facile hydrogen negative electrode reaction and electrolyte formulations that suppress Mn(III) disproportionation, it is possible to construct a hydrogen/manganese hybrid redox flow battery with high round trip energy efficiency (82% at 100 mA cm^-2), and high power and energy density (1410 mW cm^-2, 33 Wh L^-1), at an estimated 70% cost reduction compared to vanadium redox flow batteries. In this paper we present the general concept as well as our latest single cell optimization work.