A theoretical analysis is provided to describe the recently proposed ‘convection battery’, wherein electrolyte flow is driven through a battery cell to alter its efficiency and power. Concentrated-solution theory rationalizes the observation that imposition of electrolyte flow parallel to the current through a separator can reduce overpotential losses. Equations are provided that allow this overpotential reduction to be computed in terms of the flow rate, as well as physical properties of the electrolyte and separator. Model results are consistent with earlier experimental observations of alkaline convection batteries. Current-coaxial flows with relatively low rates are found to allow fine-tuned control over limiting currents. Driving electrolyte flow through traditional rechargeable battery cells could facilitate very high charge rates.