That is a fair point regarding the motion. What I haven't mentioned is I have a 3d printer so I can actually make a hard case to fit inside a bag and to glue the wires down with. I have been looking and seem to be able to get either a 10s3p 18650 or 10s2p 21700 for pretty reasonable cost for the cells, though I will need to do much more research into building packs before I will commit. The plus side is I can get a better weight distribution by doing this, plus if I get the correct size bag the controller can also fit in it (with good separation between the controller and battery).