Apple switched from high quality cells to cheaper inferior cells in recent years, not only for iPhone 15 but across all devices, going worse from year to year, I can't prove it, but from my experience this is the only explanation. I noticed that in Macbooks and iPhones (and no, I don't use fast charging/wireless charging). There was a time Apple used batteries in Macbooks that would still have 90% capacity after 1000 cycles / iPhones after 500 cycles, and these batteries would rarely swell unlike the ones used in recent years. But it is no surprise as they are cutting costs here and there, Timmy is pretty good in that. I could write a list (example plastic used on current keyboards do get shiny way faster than in older models, they even save costs by using cheaper quality plastic) about what has decreased in quality nowadays, but let's not start with that. Be prepared for things getting even worse, it won't stop from here.
Tip: We can't have control over the quality of the batteries Apple uses, but a few habits will increase the lifespan anyways (I won't explain the reasons/chemistry behind it, you need to look it up yourself if you want to know it in detail why)
1.Use AI Dente and only allow the battery to charge to 90% (80% even better), with sailing mode activated at 5%, means if you plug in your Mac, it won't pump in a charge every time the battery drops by 1%.
2. Do not let the battery drop below 40%
3. Avoid fast charging
With that you will have roughly 40-50% to use, since most Macbook Air users are light users I assume, you could turn on Low Power Mode and it would give you around 8-9 hours for those 40-50%.
Have been using that method on my iPhone 12 Mini I bought back in December 2020. It still has 95% capacity at around 450 cycles. Like I said, I'm not a heavy user.
Developing a habit to plug in at the right time might be annoying in the beginning, but once it becomes a habit, you won't notice it when doing it.
And yes you can also do like some say, just use it without thinking and change your battery after 2 years of use. But then 1. It will cost you obviously and 2. every time you drop off your device for repair, you risk someone messing things up and causing other troubles. That is why I try not to let anyone open my devices unless really necessary.
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