Swordmaker
Your claim of 1 in 10 or 12 million means 0.1 dppm to 0.083 dppm.
That is an unachievable dppm, in particular for a phone which is a large number of components.
As a chip designer specifically for Apple iphones/ipads and many other customers over 21 years, I and the companies I worked for don’t guarantee a dppm that low.
I would say a dppm of 200 is achievable at the system level, which means 1 failure out of 5000. That 1 failure can be anything, battery or otherwise, that can shut down the phone without the user doing something. Maybe Apple is better than 200. I think that if they are achieving 50, they’re world class. But I doubt it.
They aren't better than 200. There's other reasons an iPhone or iPad could fail. . . but that is the expected failure rate for just the Lithium Ion batteries, you have other components that also have expected failure rates as well that will go into making up the expected failure rates for the over all devices. The reported failure rate among the batteries on iPhones and iPads approaches that level of one in 10 million to 12 million per year. . . but it still results in several per month occurring, some of them occasionally catastrophically.