Tesla currently uses a round battery which is apparently some quasi-standard, but has now redesigned that battery from the ground up for the new Gigafactory resulting in slightly different dimensions, but still round. Obviously in terms of battery density per volume, a flat battery is more efficient than a bunch of round batteries. Cell phones and computers all went to flat batteries long ago. Not just flat packages which contain round batteries as was the case early on, but actually flat batteries. Does anyone know why Tesla's redesign from scratch of the Li-On battery resulted in another round design?