You could always measure.

I've built up two bikes with Di2, and this is honestly the hardest part of the build. It doesn't help that the wires are $20-30 each either (bullshit if you ask me.) I've contemplated creating an online database for wire lengths, but it always gets de-prioritized compared to training.

My best recommendation would be to loosely measure and then add 50-100mm. It seems like a lot, but the extra slack comes in handy. Nothing is worse that having a cable that's just barely too short.

Not sure who you are buying from but I did the same a reached out to Art's and they gave me all the numbers I needed for my bike when I ordered my stuff...

Thanks for the replies. Found this as a guideline for tri bike set up on Trisports website:

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Randy
http://www.gulfcoasttriteam.com

That battery wire length may be for an external battery. An internal battery may need a longer wire than that.