Additional note: they also did it with some Macbooks and I can tell you it had nothing to do with battery AGE. Machines that shower either a faulty or significantly worn battery would be slow. Apple considered 80% of nominal capacity to be the limit where a battery should be replaced under warranty on those, but the slowdowns started at like 50 or 60 percent if I recall correctly. By faulty I mean devices where the system scan in AST legally said “internal fault” or something. I used to refurb Macbooks.
It was noticeable in the 2012 macbook air because that model, a weird unicorn year with components that differed from both the 2010-2011 and 2013-2017 models, would significantly slow down with a bad battery even when it was connected to AC power. Literally removing the battery made it usable again. In other model years it was never really noticeable.
Additional note: they also did it with some Macbooks and I can tell you it had nothing to do with battery AGE. Machines that shower either a faulty or significantly worn battery would be slow. Apple considered 80% of nominal capacity to be the limit where a battery should be replaced under warranty on those, but the slowdowns started at like 50 or 60 percent if I recall correctly. By faulty I mean devices where the system scan in AST legally said “internal fault” or something. I used to refurb Macbooks.
It was noticeable in the 2012 macbook air because that model, a weird unicorn year with components that differed from both the 2010-2011 and 2013-2017 models, would significantly slow down with a bad battery even when it was connected to AC power. Literally removing the battery made it usable again. In other model years it was never really noticeable.