I once had a laptop whose trackpad acted erratic, scrolling left to right in a quick hyper-active fashion. The manufacturer determined the battery, around 4 years old at the time, was slightly expanding, and causing pressure upon the trackpad. The diagnostics included a screen with a grid-like box for analyzing trackpad depressions. Sure enough there was a straight left-to-right line that formed in the diagnostic tool, mimicking mouse swipes that weren’t happening; the battery was definitely to blame. But it never dawned on me what the trackpad circuit board itself looked like – and so when my friend Darius recently posted this picture it suddenly all made sense!