I thought I would share as I have already gone through two modifications for my XTR Di2 build. This is fitted to a 2015 XL Nomad CC.

I would recommend measuring several times before making the final decision on e-tube lengths.

Build 1: September 2015 (using SM-BTC1 external battery case mounted to water bottle tabs):

I used the following (from the grip to the rear of the frame):

SW-M9050R Firebolt Right Shifter
EW-SD50L 200mm e-tube
SC-M9050 Digital Display Unit
EW-SD50L 950mm e-tube
SM-BTC1 External Battery Case with SM-BTR2A (Internal Battery)
EW-SD50L 750mm e-tube
RD-M9050GS Rear Derailleur

The photos can be seen here: http://forums.mtbr.com/santa-cruz/new-2014-santa-cruz-nomad-27-5-a-906426-155.html#post12235677

I have ridden it for about four weeks and maybe 500 km of riding. A lot of shifting as I am on the return from ACL surgery so I cannot put too much power through my left knee at the moment. I finally used enough battery to drop to the 80% mark! So any doubts about charging are basically a bit misguided.

I did not like the external battery case as it lifted my bottle cage and made it hard to fit a water bottle between the frame and the shock so I thought about other ways of routing the cabling and locating the battery.

Build 2: November 2015 (using internal battery mounted in the fork steerer tube).

I bought the Shimano PRAC0085 seat post internal mount. http://www.pro-bikegear.com/en-gb/catalogue/accessories/117/spare-parts/prac0085_main/di2-battery-holder

I have now used the following bits of kit:

SW-M9050R Firebolt Right Shifter
EW-SD50L 250mm e-tube
SC-M9050 Digital Display Unit
EW-SD50L 350mm e-tube
SM-PRAC0085 Pro Internal Battery Mount & SM-BTR2A (Internal Battery)
EW-SD50L 950mm e-tube
SM-EWW01 Wireless Transmitter (mounted to down tube near bottom bracket)
EW-SD50L 750mm e-tube
RD-M9050GS Rear Derailleur

Also the correct tool: TL-EW02 for installing and removing the e-tube terminals is really important.

SM-TLEW-02 Di2 e-tube tool
I decided that the externally routed cables are better protected with Shimano’s well designed external covers (ECWC2 E-tube Cover Set).

The routing along the handle bar is slightly neater with the longer e-tube curved back along the shifter mount and fixed to the underside of the bar with a short ECWC2 E-tube Cover.

I guess-timated a 400 mm e-tube for the bottom of the steerer mounted battery to the Digital Display but I only need a 350 mm e-tube.

Using the SM-EWW01 Wireless Transmitter as a junction (it was cheaper than the actual junction and as a bonus one can send gear use data to a GPS head unit like the Edge 520 or 810), but it means I do not need as long an e-tube from the rear derailleur so I will switch it out to a 650 mm or 700 mm e-tube then cover it with ECWC2 E-tube Cover to protect it. I can also probably install a shorter 900mm e-tube from the Digital display to the junction.

Di2 with EWW01 transmitterBy the way the EWW01 is tiny, far smaller than the web images imply (you can see it just next to the bottle cage), and great way to connect the front of the bike to the RD as the longest e-tube is 1400 mm so will not reach all the way.

Sealed the steerer area with old ESI grip material:

I charged it fully last night and it works seemlessly.