Made out of ABS plastic. Holds all the connectors, wires, controller, and all three batteries… all in the center of gravity of the bike. Looks like we have a very clean 9AH pack for the Cannondale. It seems like most frames have a similar middle triangle, so this might work well. The 10ah pack will just be a bit taller. I am very excited about the progress… On to the strapping method.