A few weeks ago, Apple admitted that some iPhone 6S batteries were not working properly, causing the phones to shut down suddenly during otherwise normal use, and launched a repair program for affected consumers. But Apple hadn’t said why the batteries weren’t working properly… until this week, when it blamed the problem on air. Yes, literally air.

You might think that air is sort of, you know, ubiquitous on Earth, and you’d be right. But the wrong kind or amount of air at the wrong part of a delicate manufacturing process is actually a problem, and that’s what Apple’s pointing to.

In a recent press release (h/t The Verge), Apple writes that the affected phones “contained a battery component that was exposed to controlled ambient air longer than it should have been” before the battery packs were fully assembled. That means the issue with the batteries is due to a flaw in the manufacturing process, not in the design. So new batteries made more carefully, using the same design, should work properly.

Except… that may not be the only problem. Apple also adds that a “small number of customers outside of the affected range” are also reporting sudden shutdown issues. Apple did not say if the issue is related to the battery-draining iOS update that some users report experiencing, but to pin it down, everyone’s iOS is getting an update next week to include “additional diagnostic capability.”

With that data-gathering ability, Apple hopes to narrow down the performance issues and, ideally, be able to update battery performance management with a software patch.

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