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I wonder if Android does the same thing. My understanding if batteries is that @ 100% charge they are going to sit around a certain voltage. They will never stay at the maximum voltage under use though. Is it possible that the OS needs to drop the CPU freq due to the voltage requirements (which maybe a 70% healthy battery could NEVER hit), and ultimately stressing/draining the battery quicker at higher frequencies.

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LiPo batteries generally supply from 4.2V to 3.7V from a fully charged state to a fully discharged state. Modern CPUs run at under 2V. If the battery was directly connected to the CPU, the CPU would fry.

https://en.m.wikipedia.org/wiki/Buck_converter

That being said, it's conceiveable that a worn out battery might not be able to supply enough power to run the CPU at higher clock speeds.

Not to nit-pick, but 3.7v is the nominal cell voltage. They can supply power down to 3.3v safely. Fully discharged is around 3.0v.

Ah yes, thanks for the correction.

Electrical engineering already figured out that the voltage level vary with the charging level. It's accounted for when designing a circuit.

The voltage specification you see written on batteries is actually the discharged voltage.

For instance a car battery is known as 12V. That's the uncharged voltage, it's 14V at full charge.

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