Flow batteries have different performance characteristics than established storage technologies such as lithium-ion and lead-acid. We model advanced lead-acid, lithium-ion, and flow batteries for commercial and industrial customers under various tariff scenarios providing retail and wholesale market services to determine if flow batteries can compete in the retail market. We find that flow batteries are uncompetitive with lithium-ion and lead-acid batteries across a range of use cases and modelling assumptions. Flow batteries at a 4-h duration must be less expensive than their competitors on a dollar per installed kWh basis, often by 20–30%, to break even with shorter duration li-ion or lead-acid despite allowing for deeper depth of discharge and superior cycle life. Our results are robust to assumptions of tariff rates, battery round-trip efficiencies, amount of solar generation and whether the battery can participate in the wholesale energy and ancillary services markets.