I have been thinking to upgrade to Ultegra Di2 for my 2015 Defy Advanced Pro 1. Besides the list below, I know I still need more parts but not sure what I really need. Please direct me. Thank you in advance.


Current-->Upgrade to

Shifters: RS685-->RS785
FD: FD6800-->FD6870
RR: RD6800-->RD6870
Caliper: RS785-->N/A
Crank: FC6800-->N/A


Junction Box SM-JC41
Di2 External Battery or Di2 Internal Battery - Do I need both, or either one will be good?
Battery Charger