My wife’s Intel-based laptop got considerably slower in the last year or so. I tried everything I could but nothing seemed to return it to its original performance.
Then she got a warning that the battery needed servicing. After getting it replaced (and the Apple employee warning us several times that it might not help performance), the laptop was back to its previous state. My theory is that the battery running warmer was causing the CPU to throttle. Or perhaps cleaning out the machine while replacing the battery helped it thermally. Or maybe both.
Interesting, how old was it? Do you recall how many cycles the battery was at? Unfortunately throttling is unlikely in my case, at least for the lagging I observe day-to-day, I don't see any throttling via `pmset -g thermlog`. I did wonder if changing thermal paste would help, but since I don't observe throttling I'm not sure it would
Then she got a warning that the battery needed servicing. After getting it replaced (and the Apple employee warning us several times that it might not help performance), the laptop was back to its previous state. My theory is that the battery running warmer was causing the CPU to throttle. Or perhaps cleaning out the machine while replacing the battery helped it thermally. Or maybe both.