As I happen to be endowed with the honor to use a Specialized S works road bike that was lying in a friend's basement, I decided to go for a ride until swift realization of the gears being electronic and thus not powered. There seems to be a place to perhaps plug a battery where a bottle holder is supposed to be, perhaps one is lying around where I got the bike from. Now, I know nothing of such advanced bicycles and tend to see how certain advancements in terms of progress may seem immediately desirable but are not so convenient as I literally can't go for a ride without electricity.

I wished to know if any of you had any further insights on this matter that I could gratefully benefit from. May you be well!

EDIT : Thank you everyone for your helpful guidance, an avid cyclist told me which battery was fitting and I found it, Dura-ace Di2 !

  • Send Pics... edit
    – Swifty
    Commented Sep 17, 2020 at 19:25
  • 5
    Does your friend have any other super expensive bikes just.... laying about? bicycles.stackexchange.com/questions/63187/…
    – Criggie
    Commented Sep 17, 2020 at 19:34
  • And your friend is unable or unwilling to help you get the bike sorted out?
    – Rider_X
    Commented Sep 17, 2020 at 20:36
  • I have trouble uploading pics, maybe because I'm new to the forum bicycles ? Commented Sep 18, 2020 at 6:36
  • 1
    @AliochaKaramazov you can edit the question to include URLs to the photo and then someone with more reputation points and embed them into your questions
    – Paul H
    Commented Sep 21, 2020 at 23:37

2 Answers 2


There are three major component manufacturers: Shimano, SRAM, and Campagnolo. Each has their own electronic shifting system.

  • SRAM's is simplest to recharge: the batteries are attached directly to the front and rear derailleurs; to recharge, detach one and put it in its dedicated charging base.
  • Shimano has a "Di2 junction box" either underneath the stem or in one of the handlebar endcaps, which can be recharged with a USB cable.
  • Campagnolo has a system called EPS that is similar to Shimano's.
  • 1
    Sadly Shimano isn't simply charged via a standard USB-cable. That would be too simple, ;-) You need to plug a special connection box into the junction box that in turn is then connected to a USB power adapter or a USB port on a computer.
    – Carel
    Commented Sep 17, 2020 at 19:01
  • Because the OP didn’t state which model year S-Works, it’s possible that the junction box is elsewhere. I think the current year Tarmacs have it in the seatpost. I think some bikes put the junction box on the down tube, close to where the cables enter it on bikes with externally cabled handlebars. Also, I think the current EPS versions may only have the bar end ports (I.e. no under stem boxes).
    – Weiwen Ng
    Commented Sep 17, 2020 at 21:14
  • Thank you all for your kind help and answers, from what I see it is Paris-Roubaix model. Commented Sep 18, 2020 at 6:44
  • @AliochaKaramazov Even that information still doesn't help a lot. We need to know the MAKE of the drive-train components, especially the derailleurs.
    – Carel
    Commented Sep 18, 2020 at 7:40
  • Right, well the brand is Dura-ace and could hardly get any further info than that. My lack of expertise is visible! Commented Sep 18, 2020 at 8:10

I'll deal with the convenience of electronic drivetrains. SRAM's eTap groups have the shortest total battery life. In these groups, the shifters use a short-range wireless protocol to send shifts to the derailers. As Adam mentioned, each derailer has its own battery. SRAM claims the current AXS versions last up to 60 hours of riding time on a full charge. This is a fair amount of riding time. You could charge your batteries weekly. The CR2032 batteries in the shifters should last about a year.

Shimano's Di2 system has a battery in the seatpost, and wires connect the shifters to the derailers and the battery. This is harder to set up than SRAM. However, the battery lasts longer. A full charge can last months. I believe Campagnolo EPS has similar battery life. I have not heard about FSA's WE group, but uses wireless communication to the central processor, and wires between that, the battery, and both derailers. I'd expect similar life compared to Shimano and Campagnolo, plus you probably need to change the batteries yearly.

It's true that you now need to check battery life regularly. In partial compensation, you now don't need to deal with shift cables at all. I can assure you from personal experience that the batteries do last much longer than typical personal electronics, and other riders would say similar. They are not inconvenient once you get in the habit of periodic checks - although I suspect it can be harder to build intermittent habits than daily habits. You could set a reminder on your phone to check your batteries periodically.

In general, you can design lithium ion batteries to provide bursts of power or continuous power. I believe that electronic shifting probably uses power cells, since they would only need to produce short bursts of power to move the derailers (admittedly, they'd need to provide some continuous power if Bluetooth communication with a head unit is enabled). Our personal electronics most likely use energy cells. I've seen one page that rates the current Di2 battery at only 500 milliamp hours (i.e. it can produce 500 milliamps of current for one hour; this is a measure of stored electric energy). Each SRAM AXS battery is apparently rated at 300 mAH; I'd attribute the system's shorter battery life than Di2 to the fact that it needs to maintain wireless communication. In contrast, the current generation iPhone SE has a battery rated at 1,624 mAH, and most iPhones have larger batteries. Despite the apparently low capacity of electronic shifting batteries, they do in fact last a long time. Furthermore, the AXS batteries should charge within an hour, and a flat Di2 battery should get to a useful charge state within an hour also.

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