Thank you, HWTech for your considered reply.
In the last few days I have been using Coconut and Battery Health 2 apps to monitor the battery charge and discharge cycles. I have also been using my USB C battery charge monitor (in-line with the USB C charging cable) to minitor and tally results with what the OS is reporting. Results are conflicting.
The only reason I am here asking this question is because I noticed a sudden and significant drop in battery performance one day a few weeks ago after a couple of years of superb performance. Battery life 'felt' like it had dropped off by 40-50% from one week to the next after 2 years. So I started monitiring the mAh charge into the battery and immediately found that the battery was only takinh 2550mAh to charge from 1% to 100%. I have now repeated this 4 times and I have nearly identical results around the 2550mAh number.
Apple's literature states that this M1 Air shipped with a 4,379 mAh battery and my monitoring software (Coconut and Battery Health 2) states the 'original max' of my battery capacity to be 4,382 mAh. The software also states that the current maximum charge is 4001 mAh. So, a 381mAh reduction over the original capacity. This works out to about a 9% drop in capacity. Apple's software is reporting 88% battery 'health' - whatever than means, or a 12% drop in capacity.
However, over USB C, using the power monitor, I have consistantly only managed to measure a maximum charge capacity of 2550 mAh from flat to 100% - over a 40% capacity drop from new. I have to say, the 40% drop in capacity is far more in line with my experience of this battery suddenly loosing so much capacity in everyday use. I wouldn't have been motivated to look for explanations over an incremental 10-20% drop over time.
So, my conclusions are that the OS software is not reporting the truth. The battery has lost much more capacity than advertised and that battery 'health' is far lower that 88% in real life.
Unfortunately, I live 1.5hrs away from a 'genius' bar and my issue isn't straightforward to explain or demonstrate without having several hours to kill and a power meter. I am still will full Apple+ care coverage for a few more months but I have no idea when I'll be able to get to an Apple store and I have little enthusiasm to be lectured to my a 'Genius' about battery life and how the OS says it's healthy at 88%. I'll try and write to Apple directly for an explanation of the battery health discrepancy I am experiencing.
Many thanks.
