Can the di2 battery be run inside the aluminum seatpost that comes with the stock bike?
Is there a mount or a hanger?
Or do I need a separate seat post?
I have hidden it in the alu seat post. Wrap the battery with foam (thin foam, I got it from some packaging used in some trek parts) and tape it well. Then shove it up the seat post.
Has held up fine for me. I'm sure you could upgrade to the carbon seat post and get the adapter but IMO thats a waste of money. Foam and some tape is basically free.
Okay that's probably what I'll do I guess my only real concern is if it would slip out of the seacoast down into the frame.
My only advice is to get a longer cable than you think you need between the junction in the bb and the battery. When you lift the seat post out for servicing or if the battery happens to pop out for some reason you can easily retrieve it. But yeah, I have ridden on shitty Canadian roads for thousands of km's and it hasn't dropped out, and I did the entire installation myself.
Ty. Good advice đź‘Ť