Ultra-high rate batteries, namely iso-SC-batteries, now have been developed the second generation sodium batteries. Unlike the first-generation lithium batteries, those new generation have seen improvements in safety performance and a further reduction in cost. This paper applies sodium iso-SC-batteries to the train regenerative braking energy storage, replacing supercapacitors and flywheels. Engineering practice has proved that the energy storage system based on sodium iso-SC-batteries has a simple structure, low cost and higher safety. This technology has great potential for application in the train braking energy storage system.