Originally Posted by bahula03

Just curious where you're getting that from? My impression, and the compatibility chart TimothyH linked to agrees, is that bare minimum you just need the derailleurs. Assuming you have a SM-EW67A-E for your Junction A, probably worthwhile to go to a SM-EW90-A which will get you a USB port and let you do firmware updates on your own. The external battery (and mount) should be compatible with whatever you choose.