Consider getting what's called an “easy out" kit for small screws. These work very well. Damaged Screw Extractor Kit and Stripped Screw Extractor Set. Its A HassleFree Broken Bolt Extractor and Screw Remover Set Made From H.S.S 4341 With Hardness 63-65hrc. https://www.amazon.com/dp/B07GZ17QD9/ref...
According to the info I found here:https://versus.com/en/samsung-galaxy-s7-vs-samsung-galaxy-s9 Those batteries are the same and should be interchangable.
If you have the adapter you can test to see which blade of the plug is not powered. Looking at a picture of the plug itself on the web I can see that the outer barrel of the adapter is (-) so using a continuity tester with one probe on the outer barrel, move between the 2 blades until you get a signal, that blade of the plug is neutral and the other will be positive giving you the polarity. If you do not have the adapter you can attempt to match to the configuration shown in this photo or just buy a replacement.
Check the battery connections, they may have loosened some since it was replaced recently. Retighten all connections then check to be sure the battery has voltage enough to start the engine.
