LD150 wrote:
6 months with no drop in battery capacity (aka "Health") is very unusual. You were lucky with that 12.
Charge it all night every night to invoke optimised charging. Don't wait til it's v v low.
It's not necessarily super precise nor accurate to the minute. I too had an iPhone battery that stayed at 100% reported battery healthy for about 6-7 months before dropping to 99%. But then again battery health is an estimate, and one where the updates don't seem to be every day such that one can see every time it drops a percentage point. I've seen it go down in chunks overnight, like 3% here and 4% there where it was putting off the "bad news" for a later date. I wouldn't necessarily rely on seeing it at 99% for months since it could update at any time and drop a few percent.
Another thing is that it's based on 100% of the rated capacity. All battery manufacturing has tolerances where there could be variations in brand new battery capacity. The NiMH batteries I use rated as 2000 mAh typical are labeled as 1900 mAh minimum (of course when new). Haven't there been a few cases where battery health was reporting more than 100%. Or perhaps one where it's less than 100% and it updates quickly.
But then again I think a lot of people are overly obsessing about it. Some do worse and some do better. This is just the nature of modern battery powered electronics. The batteries that Apple uses are subject to the same limitations as any other electronics maker.