As a manufacturer they can contact directly shimano.I know of some small manufacturers who were succesfull getting motors and batteries from shimano.They were actually only assemblers not a frame manufacturer.Whope they will susceed.
Hi,how is the original battery mounted in the frame?Can you make some pictures?Diy Battery should be around 1.7kg with 20 cells for 36v and around 2.1,2.2 kg for 48v