Does anyone know what parts I need to convert a mechanical cannondale slice RS (2013) to Di2? Looks like there's no way to use the internal battery that typically goes inside the seatpost, and that I need to use an externally mounted battery under the BB. If there's a blog or post that shows the installation, that would be really helpful :)

I'm using dura-ace 9070 and have the derailleurs, bar end shifters (not using integrated brake shifters), 3-port junction box, internal battery, internal junction box, and all the cables to install internally (before I got the slice I had plans to get a bike that would allow the battery to mount internally).