Abstract: A low temperature, liquid metal approach provides a metal-air battery at room temperature or slightly above for high current density, using ambient oxygen as an electrode without the need for high heat for an opposed metal electrode. A metal-air battery employs a low melting point metal such as gallium for an all-fluid battery having a flowing aqueous electrolyte for maintaining a large volume of electrical storage capacity separate form a relatively small reactor or cell for powering an electrical load. Reversibility of the forward discharge (load powering) reaction provides a recharging capability well suited for grid storage to moderate supply and demand variations. The result is an ultra-high density, rechargeable, safe, grid-scale electricity storage technology as an alternative to lithium-ion and solvent-based flow batteries.