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I'm considering installing an Ultegra Di2 groupset on a small road bike. The space below the water bottle bosses is too little to install the regular road Di2 battery, but the XTR SM-BTC1 Di2 battery holder looks like a good option: http://bike.shimano.com/content/sac-bike/en/home/components1/mountain/xtr-m9000/sm-btc1.html

The question is, can the XTR Di2 battery actually be used with Di2 road shifters like Ultegra 6770 or 6870? Or is there some other battery offering similar mounting options for road bikes?

One reason for optimism is that the XTR battery page says "Six E-Tube wiring ports with cable organizer," which sounds perfect since the bike in question has no space for an internal wiring junction down near the bottom bracket.

The page also says it holds the SM-BTR2 battery, which seems to be exactly the Ultegra/Dura-Ace internal battery stick that goes in a seatpost.

  • John, Did you ever get this set up? did you have any issues with it? I have an older steel frame that I am debating running the SM-BTC1 on because I don't want to drill holes in the frame.. Hopeful that you were successful. Thanks, Trevor – user20335 Jul 6 '15 at 21:27
  • @TrevorH: I didn't end up trying it, but I think it will work. See my comments on Batman's answer below for more details. – John Zwinck Aug 5 '15 at 10:56
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According to BikeRadar, "The battery unit as well as the wiring for XTR Di2 are identical components to the ones used in Shimano's electronic road groups. The battery can be mounted on a bottle cage, in a seat tube, frame and can even be contained within the steerer unit of certain forks (via the use of PRO's new Tharsis components)."

  • Thanks for that. Apart from the electrical wires being compatible, what about charging? With Ultegra 6770 there is no place to plug in the SM-BCR2 charger for the SM-BTR2 battery. So if one uses this XTR battery case with 6770, how would one charge the battery? Is there some external charger I haven't found? – John Zwinck Dec 16 '14 at 0:46
  • I did some more studying and it seems that the SM-BTC1 is simply a 6-port E-Tube junction plus holder for SM-BTR2 battery. So it seems that the SM-BCR2 charger is mandatory, which in turn requires the new 6870-style "A" junction SM-EW90. So, mostly good news, unless you have the old 6770 "A" junction. – John Zwinck Dec 16 '14 at 3:20

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