I have a 2014 Specialized Crux. It is currently set up 2x11 mechanical, and it also has a dropper post.
I also have a 2x12 Di2 groupset sitting in a drawer. I have been “saving” (hoarding) it for a future frame for a few years now. I have been considering putting it on my crux, instead of not using it. But the dropper post makes installing the battery a challenge.
Does anyone have any suggestions on a creative solution to put a battery inside the frame? I do not want to use one of the bottle cage mounts that Shimano sells. Are the steerer tube battery holders okay to use with a carbon steerer? Maybe just wrap it in foam and jam it down the seat tube?
It pretty much depends on how far you’re willing to go to “hack” the battery. There’s that one video going around where the battery was literally dismembered (caveats and all that against doing so) and inserted into the drive side chain stay. That required soldering, etc.
In my case, I’ve got a bike with an ISP (integrated seat tube) that I wrapped in foam (the sort you get bundled around the tubes of new bikes), before having it lowered into the seat tube.
I had a cylinder 3D printed as an internal reinforcement (to prevent crushing the carbon seat tube) for the seat mast topper that also acts as an anchor for the cable that’s tethered on the other end, to the battery (so that it doesn’t drop further down and risk contacting the BB area, cos water, etc).
If you’re looking at inserting the battery into carbon steerers, etc, you’d have to check if the steerer tube/frame also has some means of routing the cable from the battery to the rear derailleur, cos that entire frontal area is pretty snug.
DT Swiss dropper where the top portion goes over the bottom portion? Only 60mm of travel, though, and I have no idea how much space there is in the post portion around the cable to get the battery in there, but potentially worth investigating - could work with the right battery holder or a 3D printed one that allows for the cable path to be managed..
If you’re in Australia, the carbon version is on sale at the distributor so a dealer could pass on some of that saving - they’re still not cheap despite that, though! Shout if I can help there.
I have a similar situation on my gravel bike which uses a Richey breakaway style so the seatpost needs to come out regularly so couldn’t take the battery easily. I wrapped it in bubble-wrap and pushed it down into the seat-tube, and added a wire loop so I can hook it and pull the battery out if required. No problems with it all