We are not here to advocate DIY-ing Apple products.
Just know this.
If something happens with anything with this iPad after you opened it ( like broken connections, non-functioning Apple Touch ID sensor/Hiome button,, ANYTHING ) Apple's responsibilty ends and no Apple location and even these support communities will be able to help you, any longer!
You will be totally on your own if you screw up repairing your iPad Pro.
I would just pay Apple the $99 dollars for the battery replacement cost.
Apple and Apple stores do not actually repair iPads.
To expedite the quickest of customer service, Apple only does in/out of warranty device replacements.
If Apple determines that you have a failed battery AND there is nothing else wrong with this iPad Pro,
for a $99 battery replacement cost, Apple will give you a replacement, refurbished 2016 9.7 inch screen iPad with a 90-day warranty,
The choice is yours.
Good Luck!`