Electronic & Hydraulic Shifting (Di2, Ui2, customisations)

There's some internal battery tear-down videos but I've not seen an external one.
https://www.youtube.com/watch?v=eXVhNUqRdfE

Are there electronics inside an external di2 battery ?

Yes. I stripped one down to make an internal battery before they were officially available. It's not just batteries in there.

So you need both the holder and the battery to make a custom one ? Simply supplying 7.4V to the battery holder doesn't work ?

The holder has no electronics inside. The battery does. You don't need the holder. As for whether the electronics inside the battery are necessary, I don't know. I assumed Mr Shimano put them there for a reason, so kept them when I reconfigured the battery. They might just be a charging/battery management circuit, but I'm not sure.

The holder has no electronics inside.

This thread says otherwise ..
There has to be a PCB somewhere, to manage the CAN Bus protocol

From that thread "in every part in the Ultegra DI2 group is a micro-controller so it can communicate with the other parts." answers your original question.

If you are talking about the pre-CANbus 7970 Di2, that's a different matter.

"7970 u can just cut off the battery mount and hook up any 7.4v Lipo... 6770 is the first using CANBUS, so u cannot, without putting the battery mount inline as well"

I'm talking about the CAN Bus versions. So theoretically I could buy an external battery holder, keep the PCB only, and connect my 18650 cells to it ?

Except that statement above infers that every part requires the PCB (perhaps they're assuming internal battery though).

But then someone else posts this, which implies that if you have the battery holder you can use any battery cell.

I've got an external battery to sell somewhere in the shed if you need to buy one to find the answer out.

I’ve taken one apart for some reason. I’ll have a look in the garage take some pics if I’ve still got it and pop on here

You could add a Bluetooth widget inline

You're quite right. I re-read my thread about doing this on my bike, and there are electronics in the mount. Apparently I took it apart and extracted the circuit board. It was a long time ago...

So theoretically I could buy an external battery holder, keep the PCB only, and connect my 18650 cells to it ?

There's definitely also circuitry inside the external battery. As I said, it might just be a charging/BMS circuit though.

I took the battery apart to install it internally. You need to keep the connector to the charger to make it work so hence my config with any old connector when charging.

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Thanks everyone!
I ordered a battery mount, I'll try without the battery itself and if it doesn't work I guess I'll have to buy an external battery ...
I'll give an update

All that talk of Y cables on the last page had me thinking nobody here is down with soldering irons and heatshrink.

The Shimano cable is incredibly tough, but you only need it to be like that outside the bike; you can just splice it to the inners of a USB cable (I plaited the two wires with fuzzy twine for silence). With E-tube, all the components are in parallel, so you can wire it however you like. Mind you, splicing those E-tube cables is a bit fiddly due to the amazing toughness of both layers of insulation.

Update on my battery drain: Its the left shifter. Tried every combination possible, including using different ports on the shifter. swapped out cables...etc.

Is there anything else I can do apart from firmware update and contact cleaning spray?

Can you get at the board inside the shifter? Maybe a bit of debris is short circuiting it.

Nah, its a closed system within the shifter. All the circuit boards and switches are in little boxes glued shut :(

firmware update and contact cleaning spray?

Have you done these things already? When I had gunk in my shifter it made shifting intermittent, didn't do anything with battery. I presume you've tried a different cable to the problem shifter?

Havent just yet, I'll get the spray today. I tried different cables and all that...

Another thing I read elsewhere (but didnt resolve my issue) is that if you dont disconnect from the phone app, the bluetooth module will continue to drain the battery.

I've never used Di2 Bluetooth. BT is a battery drain in any device. What is it providing that warrants it being enabled?

I want Di2 to change gears. That's it.

I can lap/pause/scroll screens...etc on my Garmin from the hoods, which is nice. But supposedly it switches off when the system goes into sleep mode after inactivity.

I already tried a combo where the bluetooth is connected, but the left shifter isnt, and in that combo there was no battery drain.

Yeah, hard no from me on that shit. My Garmin has a touch screen. Normally I just leave it on one screen.

Anyway, you eliminated BT it seems. I presume you've tried another shifter?

Finally tested with another shifter. Its 100% the left shifter thats draining. I can do two things from here:
-Buy a new LH shifter
-3D print a bar-end plug that has a switch glued into it, spliced into the Di2 cable that goes to the left shifter. This way I can disconnect the left shifter without much hassle when I get back from my rides.

Sigh...