Compare the short screws carefully before reinstalling them. The shouldered screws go in the holes on the front edge.
I found it more convenient to lay the computer keyboard-down on a table with the display hanging over the edge while performing steps 11–15.
These are just the steps to remove the battery. For the trackpad itself see the Early 2011 Trackpad guide.
On my MacBook, the screw nearest the optical drive is 5mm long.
When replacing the logic board, route the DC-In cable around the front side of the aluminum post.