2019 trek speed concept - di2 groupset update

I am thinking to upgrade my trek speed concept 2019 with di2 ultegra groupset, but i can not find specific information about the special mount to install battery inside of the seatpost. Do you know specifications, pictures or where could i buy this special mount?

Any other advice for my project will be welcome, mainly about somethink specific to install the upgrade in my bike

thank you very much in advance for your help in this matter