Internal vs external? Obviously I could mount an external under the saddle or somewhere else, super simple. Internal on a small Plasma 20 is going to be more of a challenge as the seat post isn’t designed for the battery, so I’d have to see where I could fit the battery. I think I’d be worried about it bouncing around / rattling.
My experience has been the opposite which is to say I have found positioning the internal battery much easier. I used the external battery under an Adamo saddle before the internal battery was available. Many saddles do not have enough space. I found 4 issues:
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Eventually under constant pressure the battery case became damaged, eventually damaging the battery. My wife who was riding the bike weighs about 52kg.
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Routing the cable required drilling the seat post.
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Fitting a small under saddle pack was quite tricky.
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Compared to the internal battery the external battery and harness is quite heavy.
Normally you can place the internal battery in either the seatpost or seat tube. I prefer the seatpost as it makes it easier to get it out again. Some manufacturers have developed shim kits for their seatposts. If you can get one they make sense especially for round posts.
Aero posts can be a bit trickier. On our Cervelo seatposts which are narrow I used an old road inner tube to cover the battery followed by tapered electrical tape. It is important to taper the electrical tape if you want to get the battery out again. Trial and error will guide you to exactly how much tape to use. The internal battery has a recess which allows you to make a loop with a couple of zip ties. This makes extraction easier.
With a bigger aero seatpost like my Trek Speed Concept I used some packaging foam and electrical tape.
I clean and re carbon paste seatposts every 3 months and 12 months on I have not had any battery slippage on 3 bikes.
Second question is Shimano battery vs another aftermarket battery like a Tenergy. Any reason to not use an aftermarket, it’s essentially the same type of battery in RC cars / quadcopters.
Hacking first generation Di2 was relatively easy but, became more trouble than it was worth with e-Tube wiring. The Shimano internal battery is good enough that I think you’d hit diminishing returns pretty quickly.
Lastly, does anyone have a recommended place to source all the components?
I am in Europe and used Bike24. Early last year they were the only supplier with stock of the internal batteries.
Aside of the list below, I think it’s just the e-tube wires I need to figure out. Anything I’m missing, or anything that’s glaringly wrong, just lemme know.
Rear Derailleur - Shimano Ultegra Di2, RD-6870
Front Derailleur - Shimano Ultegra Di2, FD-6770
Battery - Shimano Di2 SM-BTR2, internal (possibly external)
Aero Bar End Shifters - Shimano Ultegra Di2, SW-R671
Brake Lever / Shifter - Shimano DuraAce Di2, ST-9071
Junction Box - Front - Shimano SM-EW90-A 5 port
Junction Box - Rear - Shimano SM-JC41
You need to add the combined interface battery charger. SM-BCR2 and you will need the SM-EW90-B which is the 5 port junction. You might consider the FD-6870 front mech. I say consider because I am not 100% sure if the front mech trim option from the shift leavers only applies to the STI style shift leavers and not the TT levers.
The other thing you will want to get is the Dealer Manual from http://si.shimano.com It includes information on planning and installation. It is worth checking before you order anything. Keep in mind that as new features are added via firmware updates they update the manual. The front mech trim option is a good example.