I'll be of some help but I don't know the details... what I know is I have a P2 and just did a Di2 upgrade and the battery is stored in the seatpost. Not sure if my shop had to do anything special to make it work.

I have a P3 (which I assume has the same seat post) and the internal battery fits fine. In fact you need a bit of tape or foam round it to hold it in.

The bike shop, a Cervelo dealer, was adamant that you couldn't do it and it had to go on the down tube. Morons

What year P3?

2017

i used sugru the first time i went di2, then on second conversion back i did not and battery is now in seat tube

So it sounds like it's not a tight fit then. That was my hesitation, that it would need to be crammed into the post & risk cracking the carbon.

Nope fits in easily. Mine actually fell out and I had to tip the bike up to get it out. I wrapped some masking tape round the end to hold it in place.

I read you can also wrap it in the foam packing bikes ship with, which I have plenty.

FYI, for the P2 (I have a 2017 or 2018) you can use the Pinarello F8 / F10 aero seatpost Di2 battery internal mount. *At least with my EPS battery.

---

- Jimm