Can't diagnose erratic trackpad behavior
Some time ago this computer started exhibiting erratic behavior related to the cursor/trackpad: unresponsive to inputs; cursor jumping around on screen; phantom clicks.
My wife took it the Apple store and they claimed to be unable to identify any fault. (Amazing.)
The first thing I did was a full wipe and OS install. That didn’t change anything.
Then I did some experimenting and found that the problem would only kick in once the battery had reached around 35% charge. I took this to mean that it was a swelling issue (a commonly reported cause) and a new battery would fix the problem. So before buying one, I swapped in a compatible battery from another MBA and, though things worked fine at first, eventually the problem returned.
I’m now at a bit of a loss. I could buy a replacement trackpad, but who knows if that would work. Also, why would things be fine even with the old battery at a low charge, but not at a higher one and not with a separate battery altogether (that donor MBA, by the way, was always functioning fine)?