Battery aging and safety - M1 Macbook Pro

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Battery aging and safety - M1 Macbook Pro

Hello there, everyone!

I use an external monitor with my macbook constantly, and it's plugged in through an adapter that also passes through power from the original macbook power adapter.

Since the whole setup was built around a 2018 Mac Mini that I just exchanged for the M1 Macbook (because I wanted to upgrade and, in theory, need a laptop now that I didn't before), I've been using the macbook in Clamshell mode, and for it to work with my external HDMI monitor, the macbook needs to be plugged to power.

My concern is if this is safe for the battery, both in terms of causing damage or problems such as swelling (had that happen with 2 Razer Laptops plugged to eGPUs in the past), as well as in terms of battery longevity, since the macbook is basically between 90-100% charge all the time.

Sometimes I see that the power is plugged in but the Macbook isn't being charged, and the battery just goes down a bit to like 92-90% and then it starts to charge back up to 100%, but overall, I'd consider this to be a situation where I'm constantly keeping it at full charge, and I'm worried this might not be good.

I've read a bunch of people saying it'd be ideal to cycle a bit of the battery, letting it drain to about 30-40% and then charging it back up at least once every 2 days, but to do that I'd need to not have the macbook in clamshell, since when not connected to power, it doesn't work with the external monitor.

If that's something I *need* to change in my setup in order to play nice and take care of my macbook, great, so be it, but I'd like to understand a bit more of how this whole thing works, since there isn't a way to "make" the macbook bypass the battery and use the power from the wall directly if/when I'd need to (or want to).

Any help or info would be greatly appreciated.

Thanks!

MacBook Pro 13″, macOS 11.2

Posted on Mar 17, 2021 8:04 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

133,369 points

Mar 17, 2021 8:11 AM in response to Gustavo Gonzalez

That computer is a battery-CAPABLE device. It is not optimized as a battery-operated device.

Your computer performs best when connected to AC power. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, even with the power adapter connected, the charged state may even decline during stressful work.

When used only on battery, your computer has no extra cushion of power, and will perform more slowly. However, for ordinary non-stressful tasks this may not be objectionable (possibly not even noticeable.)

In general, you should ALWAYS connect AC power when it is possible to do so, and only run on batteries (which will be somewhat slower) when no AC sources are at hand. There are three micro-controllers cooperating on battery and charging issues, and your Mac will NEVER over-charge.

An external power supply that provides "USB Power Delivery" (like certain displays) can not 'force itself' on your Mac. The Voltage and Current are delivered only after your Mac requests and the charger agrees to supply power under certain controlled conditions. The computer is in control of the entire process.

A charge cycle is ever-so-slightly destructive to batter longevity. When operating as designed (and not using Battery Health Management) battery charge level is allowed to decline to about 92 percent level before initiating a recharge cycle to top up to about 99 percent.

————

Catalina software 10.15.5 and later for MacBook Pro with T2 chip (2016 models and later) includes a new feature called Battery Health Management. Based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop before 99 percent.

About battery health management in Mac notebooks - Apple Support

https://support.apple.com/en-us/HT211094

This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging may stop short of 100 percent charged. Recharging may only begin at a lower level than the previous "normal" threshold of 92 percent or less.

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Answer 2

Mar 17, 2021 11:52 AM in response to Grant Bennet-Alder

First off: thanks for the response!

Anyway, yeah, most of what you brought up makes sense to me and from what I know of notebooks, but having had 2 notebooks (granted, from another brand) have battery problems caused most likely from being connected to power all the time to be able to output to an external monitor, my main concern revolves around the idea of having the macbook plugged to the monitor *and* power all the time, vs having it plugged to the monitor but not in clamshell, hence not necessarily also to power, and manually removing the power source to let it drain the battery to like 30-40% (not until dead) and then powering it back up.

I mean, all the battery health management stuff is turned from default since I got it, it's all at 100%, so great... But is the battery isolated from when it's at full?

What I mean:

Power is drawn, so if the machine pulls 65w, it'll get 65w from the source (if it can provide, obviously), and if it needs less, it'll just draw less. So far, so good...

My questions then are:

1) let's say the battery is at 100%, and you're using less or exactly as much power as your source can deliver to the Macbook.... Will the Macbook use the battery and simultaneously replenish it from the power source OR will the system "isolate" the battery and use the power directly, bypassing the battery?

(I'm under the impression it does that on its own, but only up to that 90-92% threshold, and from there, it'll just start recharging again.)

2) But if it does that, I imagine it'd mean its prepared to work properly in those conditions without that being an actual problem... Which then poises the question: Why do so many people get close to yelling out that keeping batteries at 100% (or too close to that) is bad for the battery, hence you should make sure the battery flexes (discharges and recharges) partially like once every 2 days, at least?

Thanks!

Oh, and on the performance side of things: I'm aware of the potential loss of performance, but haven't been able to quantify that close to at all with the M1 mbp. Performance has been basically identical on power or battery, doesn't matter what I'm doing.

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Answer 3

Mar 17, 2021 12:04 PM in response to Gustavo Gonzalez

An external power source cannot "force itself" onto battery charging. The battery gets at most a minuscule charge, unless a 'charge cycle' is initiated. This is all controlled by multiple micro-controllers, very carefully and deliberately.

Your Mac will never over-charge.

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Battery aging and safety - M1 Macbook Pro

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