Hi @matfrags
I love the idea as I know that Samsung batteries tend to be cross compatible.
Your biggest issue unfortunately is that Samsung significantly changed the connector location between those generations so it will be practically impossible to connect the Note 9 battery once it's installed…
My recommendation in this case is to stick to an original quality replacement battery that you know will work so you don't need to open this phone again once it's repaired and working
Hope this helps!