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Comment by gambiting | Hacker News Reader

That's because older MacBooks could draw more power under 100% load than the power adapter could provide. Instead of shipping with a bulky 90W adapter, apple decided that 65W one is sufficient for almost everyone, and if you need to run your machine under 100% load it would just draw extra power from the battery. Hence, if you don't have a battery or its dead, the machine will never allow 100% load(this might be different if you actually plug in a 90W adapter, but I don't remember the details now).

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So it was literally impossible to run the device at full load for extended periods? Presumably the battery eventually hit 0 and the devices was then power limited? That's insane. I assume thermals prevented it before the battery did, however for premium devices, it seems like a profit protection measure for Apple, rather than a cost saving feature for uses.

If the battery was full and you were running at full load it would take over 5 hours to discharge the battery to zero - and if you are running CPU+GPU at full load for over 5 hours on a laptop then I'd say you are probably on a wrong device for this. I'd take a smaller (lighter) power adapter + max 5 hours of full load than a heavier adapter and unlimited full load. I actually know someone who carries a 45w adapter with his macbook 15" because it's smaller and the laptop runs from it fine unless you run some heavy loads on it - for normal browsing/coding work it's fine.

Lenovo did (still does?) the same thing. My old T420 shipped with a 65W charger but required 90W peak power to run at full clocks. At some point it decided that even with the battery in place and fully charged that it will only run throttled down to exactly 800MHz! With the cpupower tools I could make it run at full 2.7GHz but without frequency scaling of any kind. It was either 800MHz or 2.7GHz.

This happens to a first gen retina macbook pro. So not sure if they stopped doing this.

I don't see battery life going down when plugged in on a current MBPr15, even when torturing it w/ recompiling all my ports tree.

Maximum CPU load is not enough - you'd need to run full load on cpu, GPU , hard drive and have the display on full brightness - it really is an edge case.

Gaming. Though that's usually not done at 100% brightness. IIRC my mbp with geforce 750 came with a 90W adapter, but that would also not be enough when running the 45W CPU and the 35-40W GPU at max with ram and screen power usage.

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