My MacBook battery began to fail and expanded to the point of temporarily deforming the aluminum near the trackpad.
Using the iFixit Pro Tech Toolkit, I followed the instructions in the step-by-step guide. The battery charged in a few hours and proceeded to work fine.
In the event that the battery swells, remove the screws from the case closest to the failing section of the battery. Use a flat tool to carefully help the battery case out of the machine if the swelling is enough to deform the case.