The 2nd battery is not in the seatpost; it’s attached to the seatpost.
The photos in the OP show you how the battery is mounted.
I completely understand your perspective at your point in life. My kids are all grown, so my focus has been gradually shifting back to what I want. You'll get there too.View attachment 62779It is sort of amazing what 2 kids and age do to you. I could truly care less what color the bike is. Having 2 choices makes me donate a second or 2 of my limited brain power to the decision. These decisions are usually left up to my 3 year old. Thus my current bike is rocking a unicorn bell and a small speaker so that baby shark and the wonky donkey can be sung along with.