Internal battery for Di2 ultegra DIY

[Kingston]

I've searched (WW and google) to find a way to make an internal battery for my Di2 ultegra.

I have another where I easily installed an DIY internal battery in the seatpost, but it seems to more difficult with Ui2.

A battery from vapextech, a new connector and some soldering, worked perfectly.

I see some threads here on WW and on fairwheel, slowtwitch and cervelo forum, but haven't found anything that can help me.

Have anyone found out how to install an internal battery for Ui2?

[Cyklus]

The new 9070 seatpost batteri is an option i think