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iPhone 15 can limit battery charge to 80%. Does this mean there’s now battery passthrough?
(www.macrumors.com)
this post was submitted on 19 Sep 2023
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The charitable thinking was that it’s only on the new models because they actually modified the power delivery circuitry to allow bypassing the battery for power. As in, a reasonable hardware limitation that prevents any older models from doing it.
The less charitable thinking is that it’s arbitrary software lock, which is unfortunately not entirely out of character for the Apple either 😅.
When you plug your phone in you are already “bypassing” the battery. It’s just how batteries work, they can’t be powering a device while being charged at the same time since the current can only go one way at a time. Batteries can’t charge and discharge simultaneously. So what happens when you plug your phone into power is that the Power management circuit directly powers the phone and excess power charges the battery.
It’s just a software decision only the people in charge at Apple know why they would limit this to new models.
You’re right that batteries can’t be both in a “charging” and “discharging” state at the same time. However, a workload drawing 1 A from a battery and a charger supplying 2 A leads to net gain of 1 A, aka “charging”.
It isn’t both charging and discharging, it’s just in a state of charging, despite the workload it’s performing. Likewise, the battery can provide 2 A while only being charged 1 A, leading to a state of discharging.
So, a battery can totally power a device while simultaneously being charged, which I believe is how iPhones currently operate. The battery is always in the power path. Willing to be wrong, that’s just my current understanding.
The battery is not always in the power path. I thought that was how it worked for a long time but got clarification from a writer at anandtech who used to do SoC deep dives. When plugged in the iPhone is directly powered by the wall adapter, excess goes into the battery.