I’ve had my MacBook for just over three years (just past AppleCare, alas), but recently the trackpad had been acting up. I couldn’t get it to click and drag at all. Opening up the case showed me that the battery was getting a bit, well, tubby — something that apparently happens as Lithium Ion batteries age.
I finally ordered a new one, and it came today. It’s nearly 50% slimmer, and sits flat on the table, unlike the old battery. My trackpad works perfectly again.
Strange, never heard of swelling lithium batteries before.
That’s how LiPos tell you they are failing.