As it happens, I bought my son the bike. I can say with some confidence that the battery provided is D3611D.

... "luna cycles" ....

While certainly worth checking, it seems to be a different battery than used by any of the motors they carry, so color me skeptical. I imagine that means paying a serious premium via Tern (since even Bafang USA said they had no information about the M400 (since they don't carry it, I guess it's OEM only).