- Some iPhones in this generation began randomly shutting down as their batteries aged.
- While looking into this, Apple determined it happened because certain aged batteries could no longer deliver enough current to sustain peak workloads (computers use more current when performing more intensive tasks). This is probably due to Apple underprovisioning the battery capacity in this generation, but that's not something they could fix in existing devices.
- Apple added a mechanism to detect when these random shutdowns occurred on a specific device due to insufficient power from the battery.
- Once the random shutdown had been detected on a specific device, that specific phone would instead throttle its CPU when the system was under heavy load to prevent the random shutdown from occurring.
In short, your phone was not affected unless your battery had already degraded and was experiencing power-related random shutdowns. The changes Apple made to deal with this were an unequivocally user-friendly change to work around a hardware shortcoming and keep peoples' phones working well for longer than they otherwise would have.
The mistakes Apple made were:
- Designing the phone hardware with barely enough battery capacity, such that some moderately old phones might not be able to keep working properly when the batteries decayed.
- Not being transparent with the hardware design flaw above, such as proactively replacing any customer whose device was being affected by this flaw while still under warranty.
- Not going far enough with the software changes to initially add something like the battery health info they later added in response to this PR fiasco.
That's about it, I think?