Lol reddit, amused that link had someone called "Adolf-Intel" participating. What a wonderful place that community must still be.

Have been meaning to dig into that situation a bit more when I saw it pop up at more trustworthy sites. My old 6s had the faulty battery issue which Apple is covering for 5 years. It makes me wonder if their attempts to address that issue in software/firmware first helped contribute to this new report. The behavior my phone would have is that it would hard shut off as if the battery was unexpectedly going to lose voltage immediately. Then waiting a few moments, would still power back up and boot fine, and come back with an estimate of 40% or so.

Since the fault was happening before the 20% low power mode option exposed to users, it was occurring while the phone was likely still allowed the system to drive the CPU to it's maximum power usage. And this was a generation of processors right before Apple introduced their variant of big.LITTLE architecture. With the 6s still on sale as a new device due to Apple's amazing lead in the CPU space, it may see an update to address this in the coming month or two.