Chosen Solution
So I followed the instructions and replaced the battery on my MacBook but now after starting it the keyboard and mouse won’t work. The power key does to start it up, but after that no input plus the fans seem to go up to full speed and stay there even if I plug in a USB keyboard just to get into the thing.
Review Steps33 & 34 in this guide MacBook Pro 15" Retina Display Mid 2015 Logic Board Replacement make sure the cable is fully seated. You may find using a small strip of electricians tape stuck to the ribbon cable can help you guide the cable in using it as a pull.
