A battery assembly including: a plurality of prismatic battery cells; first and second fluid manifolds; and a plurality of corrugated flow plates interleaved with the plurality of battery cells, each the flow plates extending from the first manifold to the second manifold and providing an array of flow channels for carrying fluid from the first manifold to the second manifold, wherein each plate of the plurality of corrugated flow plates is an extruded plastic structure comprising first and second fluid impermeable sheets and a plurality of parallel ribs between and connecting the first and second sheets, said plurality of ribs forming the array of flow channels.