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I have a 2023 16" MacBook Pro (M2 Pro). I'm trying to determine some levels of minimum charging requirements.

It's well advertised that to Fast Charge, you need the 140W charger and to use the MagSafe port. It's also well advertised that you can charge (not "Fast Charge") with the Thunderbolt ports, as per older models.

What I'm looking to understand is some level of minimum wattage necessary for, say, very slow charging. Or just maintaining current battery level. I understand this can vary under heavy usage, so there may not be a fixed answer. I wouldn't concern myself with that, except that sometimes poorly behaved apps will generate a heavy load when the user isn't doing anything special.

Would you expect an older 96W charger to be sufficient, for example? What about something even less powerful?

nohillside
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tilthouse
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2 Answers2

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What I'm looking to understand is some level of minimum wattage necessary for, say, very slow charging. Or just maintaining current battery level.

Use the charger specified for your Mac model

You can't "manage" the charging rate of your device at the charger level - that's not how it works.

Your Mac and the charger (USB-C PD compliant) will negotiate the current that gets delivered. In short, your Mac asks, the charger responds, and if they agree, power is delivered.

The power consumed by your Mac will vary depending on what it's doing. If it's off or idling, it may not draw much. If you're rendering video, it'll likely draw as much as it can. When you put a lower wattage power adapter in an attempt to manage the charging rate, you're limiting the ability of your Mac to efficiently manage power/performance.

Power is drawn from the charger, not pushed to the device

Would you expect an older 96W charger to be sufficient, for example? What about something even less powerful?

The more wattage the better. Having the ability to draw more current on demand will always be a good thing. When you get a lower wattage charger, once you hit the limit of what it can deliver..well, you hit the limit.

Below are some additional Question/Answer Posts on this topic for further reading.

TL;DR

Get the charger that was specified for your Mac or better yet, one with more wattage. You shouldn't be trying to manage battery health nor performance especially from the charger perspective as the wattage rating will not change what the device needs. Besides, Battery Health Management has been a built-in thing since Catalina.

Allan
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  • Just to clarify, I'm not asking this to try to "manage" the battery myself, maintain battery health, alter performance, or otherwise "outsmart" the built-in system, Apple's recommendations, or anything like that. However, there are times when what is available is not the recommended Apple charger. I'm just trying to get a feel for what various limits would be under less-than-ideal circumstances. – tilthouse Jun 23 '23 at 18:12
  • Even so, the answer is still correct - it is grounded in Ohm's Law. The current is limited by the device. You can have as many or a few watts as possible in the charger. The current flow will be dictated by the device itself. – Allan Jun 23 '23 at 18:16
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There is no minimum charging requirement. The MacBook Pro Apple Silicon machines will idle and run for a very long time when there is no work to be performed. Also, there is no minimum as they will charge up to 80% in any case where there is USB-C power being delivered whether it's a charger capable of 18 watts or 160 watts.

The real question is how well do you know your power budget - what tools and software will you run and how intensive is it.

  • Are you editing 8k video constantly at the highest display brightness and running XCode builds in the background? You might very well outrun a charger that's not powered as much as Apple offers.
  • Are you doing light video editing, light web browsing (50 tabs - most well behaved and not churning in the background), many office type apps, photos, messages, calendar, etc..? You might be fine with a 35 Watt charger that also powers a phone or iPad in addition to your MacBook Pro and have all day life on your battery and not deplete it at all yet have it for occasional bursts that the slower than full charge recovers in 30 minutes of light charging.

There is no general rule here, but hopefully my and Allan's answers help everyone not worry about power so much and focus on how they manage the workload. Worst case, you need a full charger and have to get a battery if your charger can't provide enough power for high power uses. There are dozens of battery packs that will run several of the highest power Macs for days if needed, and they are not light weight or low cost.

The good news is Apple's power usage tooling in Activity Monitor will let you know exactly what uses power so you can stop it or plan for the charger you need to meet your needs. The hardware itself can run a lot of work for very low power. That's the entire reason for Apple Silicon - to be power efficient all the time it doesn't need to run at high power.

bmike
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