I ran into the same issue trying to use some very small batteries that will slip inside the frame near the bottom bracket of my Tarmac SL4. I connected my batteries through the battery mount (with alligator clips) and this does work, verifying that the ID chip is in the battery mount.
The mount itself is 24.5 grams without the easily removed hardware. It is much too big to go inside my frame and is glued together - I don't think it can be taken apart without cutting it up. It may be possible to remove the circuit board by destroying the plastic housing.
Besides the cludgy stock mount and saving battery weight (mine are 21 grams for the two) I would like to be able to play around with additional shifter switches. I connected an oscilloscope and the signals are evident on top of the battery voltage. I can't tell if it is actually a CAN signal - it says so in various places on the internet but it is difficult to tell if one person made this up and got copied. If so it would not be very difficult to hack.
Chiva, please keep us posted on dismantling the battery mount!
I don't know if this image will work.