Have found a new more efficient cell configuration and package: Still LiFePO4 cells; the new configuration proposes 24 units of 3.2v 100ah prismatic cells connected in series. to give an overall 76v 100ah pack, 3C continuous (5C peak). This package along with a BMS fits into a 420 x 280 x 250mm dimensional envelope. This is substantially reduced in comparison to the old headway cells. Info below: