Not certain yet but I think this is pretty easy.
Part I mounts directly to battery on the end with the led indicators then bolts (J) and spacer (D) are used to attach in downtube on bottom bracket end.
Upper mount requires removing battery handle and then attaching mount part (A) from first photo by removing battery cover screws and securing the mount part (which mounts to the 2 holes in the upper downtube) directly to the battery cover. I think the parts B,C,D from the second photo are just part of a kit (
Darfon Battery Holder ) and not used in this application.