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I leave my MacBook Pro on my desk nearly all the time, connected to the charger with the lid closed, connected to an external display. I've heard this is bad for the battery health, and everyone in my office have to replace swollen batteries every couple of years. I want to regularly discharge the battery, per Apple's recommendation, but I don't want to physically unplug it because that temporarily turns off the external monitor, and then I have to reconnect the monitor. So I am looking for a software method of disabling the power input, to force the laptop to discharge its battery to 20% and then re-enable the power input.

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    You got an Apple "recommendation" from the "Internet Way back Machine" which dates the article around 2011 - 7 years ago. Batteries have changed significantly since then.
    – Allan
    May 15, 2018 at 0:17
  • It's possible that old advice no longer applies, but it's still a good question, and not a duplicate of that one at all.
    – Elliott
    May 15, 2018 at 0:26
  • If you look at the recent version of the page at apple.com/batteries/maximizing-performance you won't find the recommendation to discharge any longer.
    – nohillside
    May 15, 2018 at 5:37
  • macOS already stops charging at c. 80% if you leave it plugged in for a few days. There's no need to do anything.
    – benwiggy
    Jan 26, 2023 at 11:54

2 Answers 2

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Short answer

To the best of my knowledge there's no consumer software capable of doing this.

Long answer

Using software to disable the power input until your MBP is discharged to a certain level wouldn't actually achieve your ultimate goal (i.e. avoiding your external monitor from being temporarily disconnected).

That's because disabling the AC power input (or more specifically, switching it from AC to DC) is exactly what's causing your external monitor to behave in this way, and there's no way for the hardware to discern why the AC power input is gone. In other words, it's not capable of telling the difference between an AC source being switched off, a power lead being unplugged, or some software just disabling the AC power input.

The only other way to try to achieve this is to get your MacBook Pro to use more power than what the charger is supplying for a period of time. While that's theoretically possible, in practice it's just not going to happen without something that will also act to override the System Management Controller (SMC).

To explain that a little further, to get your MBP to try and use more power than is being supplied would involve stressing out the hardware, at which point the SMC kicks in to protect it, so any software would need to try and bypass the SMC as well. While it is possible to bypass some functions of the SMC, I really wouldn't recommend it, and in this case it's likely to cause much greater long-term problems than a swollen battery or a short-term problem like a disconnected external screen.

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You can use Energiza Pro to do this for you. It supports Apple silicon MacBooks and has a discharging feature. (Disclaimer: I'm the developer.)

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    People need to stop buying this stuff. One thing is to monitor your battery, but somehow people believe Apple engineers build a fantastic machine then drop the ball completely with respect to battery charging. The only thing this software does is “click to discharge your wallet.”
    – Allan
    Jan 26, 2023 at 13:47
  • Hi Allan, thanks for your feedback. Still, I have to disagree. For sure Apple engineers do a fantastic job. But, you have to keep in mind, that Apple put focuses on usability. Sure, you can let the macOS do its job. And it will probably do a good job for many of the users. But, in case you use your MacBook primarily as a desktop replacement it will not. Your battery will be charged to 100% all the time. And this wears out the battery, soon. I experienced it myself. The battery only had ~100 cycles but was dead. So I build this for myself. Sure, it's not useful to everyone. Jan 26, 2023 at 18:48
  • No manufacturer charges a battery to 100%. A full charge as indicated by the OS menas from 80-90% of the actual capacity. So if you’re stopping charging at 80%, you’re in fact charging the battery to only 65% raw capacity. This does nothing positive for battery life. What you had was a defective battery - it happens unfortunately.
    – Allan
    Jan 26, 2023 at 19:01
  • Hi Alan, I won't disagree with you on this point. But, even if Apple only uses 90% raw capacity, it will harm. I won't go into the physics side here. But, Apple is bound to the laws of physics, too. Hence, they introduce "Optimized Battery Charging" for all their devices. It charges the battery to 80% and only charges to 100% right before you need it. In case you are like me and use it connected to a charger all the time, there is no need to charge it to 100% in the morning. Also, Apple suggests keeping the batteries at 50% in case you don't use them for a longer period. Jan 27, 2023 at 7:28
  • I can understand that people prefer usability and don't care too much about their batteries. In the end, you can always replace it. But, if you do care, here is what Apple suggests: apple.com/batteries/maximizing-performance And apps like Energiza can help you do this. I'm using a display that also charges my MacBook. For me, it is a great help to limit charging in this case. Jan 27, 2023 at 7:32

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