My track pad was difficult to "click". I've replaced batteries before, so I knew that it was definitely a swollen battery. However, when removing the damaged, swollen battery, I used the end of a flat head screw driver to pry up the battery connection... DON'T DO THAT! I saw the tiniest of sparks around pins 4-5-6 on the 9 pin battery connector. New battery installed, but the OS didn't recognize the new battery -- black "X" over the battery indicator. Further, the wall charger would not recharge the new battery. Instead, the computer ran off the 30% charge that new batteries are shipped with. I ordered another new battery, and after draining a second battery without being able to charge, I figured that spark was the sign that I fried something in the logic board. Indeed that was exactly the case, and logic board replacement did fix the issue. I found these instructions INVALUABLE in replacing my old logic board.

$260 lesson: Always use a plastic spudger when dislodging connectors in computers!

Thanks!