Originally Posted by Larry77

--Only need one battery, your frame should be "Di2 ready" if you want to use an internal battery.
--You need a Junction A and a Junction B (either internal or external version depending on how you run wires).
--Need wires to run from both shifters to Junction A, from Junction A to Junction B, from the battery to Junction B, and from each derailleur to Junction B

--You don't need to change cranksets unless you want to, they are not Di2 specific