MacBook Pro 16-inch M1 Pro: 140W adapter power connection issue

kutz777 wrote:

I understand that macOS manages battery charging automatically and that keeping a MacBook connected to AC power is normal. My concern, however, is not simply that charging stops at 100%.

The issue is that, when my MacBook is asleep at 100% charge with the original Apple 140W adapter and MagSafe 3 cable, the green MagSafe LED repeatedly turns off and on, often accompanied by charging sounds.

I don't 100% agree with Grant Bennet-Adler about this behavior at 100% charge level. A Mac laptop (and this has been true of the more than a dozen Mac laptops I have utilized over the years) should not be rapidly cycling between charging and not charging with the charging sound/beeping when it reaches 100% charge level. And even with Apple's battery health management, the laptop will occasionally charge to 100% and stay there for some ~ hours, and the user should have the option to charge to 100% in advance of an extended period off the charger (it is a laptop, after all, it is designed to be used that way) without having to listen to constant beeping and changing lights on the connector from charge cycling on/off rapidly. That is not nominal behavior.

That said, I don't see a compelling need to do repairs on your Mac, I do agree with Grant Bennet-Adler on that point. Your "use at 80%" seems like a reasonable workaround, and I suggest you try increasing the charge limit to 90% or 95% just to see if that objectionable behavior (beeping, charging cycling rapidly) does not return and to see if it is only occurring at 100%. Use of a power supply that is much lower than 140W may result in slow discharge of the battery even when plugged in, depending on how it is being used. But that's up to you.

Especially interesting to me is your observation:

"The same Apple 140W adapter + USB-C to USB-C cable

MagSafe was completely disconnected.

During sleep at 100% battery, the logs repeatedly showed:

smc.sysState.USBPlugEvent ... acdetach

These events occurred approximately every 13 seconds, although the log continued to report Using AC (Charge:100%). I did not observe the same charging sounds as with MagSafe."

Based on the lack of charging sounds (beeping) here, I am suspecting that the faulty part is either the MagSafe cable that goes from the charger to the laptop, or the charger itself, but I think that MagSafe cable is more likely. Setting the laptop to charge to 100% (as one might do before an extended time away from a charger, such as an airplane trip) should not result in constant beeping from on/off charging. I think the 13 second intervals for those other messages you see in the logs may be simply the Mac checking the charge level to see if it needs to charge back to 100%. If so, that is nothing that needs "fixing."

What I would do if I were you:

• Set your automatic/optimal battery health management to "on" and use the laptop connected to the charger whenever possible. Remove the 100% charge limit.
• See if the problem occurs if/when the laptop automatically goes to 100%. It will eventually settle to ~ 80% on its own but that may take some time (weeks).
• If it does occur at 100% and it is disconcerting, you can lower the limit to something below 100% where the beeping etc. does not occur.

If the laptop still does not function properly at 100% level (beeping, light on/off/changing) with the MagSafe, consider getting a new MagSafe cable. If that does not solve it, consider getting a new 140W charger.

If the problem still persists with a new cable/charger, then there is a possibility that the MagSafe port on the laptop is not functionally properly. In that case you can switch to charging via a USB-C to USB-C charging cable, which you know is free of the beeping from on/off charging frequently.

Unless your battery provides poor usability (e.g. charge away from the power supply only lasts a very short time), I would use the laptop with one of the above reasonable workarounds. Any "repair" or even a battery replacement does not seem called for and will be invasive and you would then risk further complications, especially if you don't have access to reliable Apple Authorized Service Providers.

Welcome!

This seems a bit odd for a 16-inch (2021), M1 Pro:

• Battery health: Normal, 100% maximum capacity, 12 cycles

Is that the original battery? If so, those stats look very suspect for a Mac model that was discontinued nearly four years ago. Has the battery been replaced? If an old battery or a non-Apple replacement, that could be a factor but doesn't explain why the same battery is happy with a lower-power charger.

From your thorough report, it sounds like it is something within that charger. My M4 Pro 14" has the 96W version and has worked without issue for over 18 months. The only other test option I can think of is to replace the removable AC wall socket adapter with Apple's 6-foot Power Adapter Extension cable. I've accumulated four of these treasures, and at US$ 19, they are too useful not to have with your kit.

Power Adapter Extension Cable (AC Connector 2)

You'll need the "2" version"for the 140W adapter. They are great for travel where you never know how far an outlet may be from where you would like to use your Mac.

Did replacing the 140W adapter, changing the MagSafe cable, or updating macOS resolve the issue for anyone?

I don't see every post here but I see a lot of them. I do not recall a similar issue reported here.

Keep us posted, please!

Cheers!

Allan

Thank you for your follow-up and for pointing out the warranty considerations.

I purchased the MacBook as new in March 2026 from a third-party marketplace seller, not directly from Apple or an authorized reseller. I'm currently in Russia, where access to official Apple hardware support is limited. I have already contacted Apple's local phone support, but they were unable to provide technical assistance for Mac hardware.

I understand your concern about the battery potentially having been stored for several years. As far as I know, it is the original battery. Apple Diagnostics reports no errors, and macOS shows normal battery health, although I understand that this does not completely rule out an age-related issue.

I also have an important update from a new controlled experiment:

• With the original Apple 140W adapter and MagSafe 3 cable, I set the battery charge limit to 80% and disabled Optimized Battery Charging.
• After charging reached the 80% limit and the MagSafe LED turned green, the MacBook remained asleep overnight for over 9 hours. There were no LED interruptions, charging sounds, or recurring power connection events in the pmset log.
• The next morning, without disconnecting the adapter from the wall, I increased the charge limit to 100%.
• After the battery reached 100%, I put the MacBook to sleep again. Within 20 minutes, the green LED started turning off and on again, with charging sounds.
• The new pmset log confirmed repeated USB-C_plug wake events and brief transitions between battery and AC power.

This suggests that the issue is strongly dependent on the battery reaching 100%, rather than simply on charging being paused.

I will check the warranty coverage available for this device and continue looking for an opportunity to test another known-good Apple 140W adapter before considering any internal repair.

Do you think this 80% versus 100% behavior could point to a macOS/firmware power-management issue, or could an aging battery still explain it?

Thanks again for your help!

kutz777 wrote:

I purchased the MacBook as new in March 2026 from a third-party marketplace seller, not directly from Apple or an authorized reseller. I'm currently in Russia, where access to official Apple hardware support is limited.

It seems that this is not really a new Mac, in that case. In fact buying from a non-authorized reseller could result in a Mac in almost any state. I doubt you will get any warranty coverage that you can utilize.

Your battery is not behaving nominally. But the pedigree of your Mac is also unclear, given how you described how it was obtained "as new" despite being a 5 year old model.

This could also well be a charger problem. Those chargers are easy to obtain online, I would get a new one from a reputable supplier. The fact that your problem occurs both with the USB-C connector and with the MagSafe one seems to implicate the charger itself as the common piece. There could also be a wall socket/power problem as well as AC power cord problem. A new charger will come with a new power cord.

Try this: download CoconutBattery (I believe there is a free version) and run it, select "Battery Info" and report what it shows (without the serial number). Also click on Mac Info and report what it shows.

This suggests that the issue is strongly dependent on the battery reaching 100%, rather than simply on charging being paused.

A good battery should never behave that way. But there are other possibilities, as I and others have pointed out.

You are at a disadvantage here because you have a gray market Mac; plus, it appears to be 5 years old, at which point some people might consider it to be time to consider replacements as hardware can start to wear out after 5 years.

Thank you for your detailed reply. I agree that the 80% charge limit is a reasonable workaround and that invasive repairs would be premature.

I have two new test results:

• Apple 35W adapter + the same original MagSafe 3 cable, at 100%: During approximately 23 minutes of sleep, the pmset log showed no recurring power connection events. I also noticed no LED flickering or charging sounds when checking the MacBook.
• Apple 140W adapter + MagSafe 3, at 100%, after updating to macOS 27.2.1 (26B131): The problem returned within two minutes. The log again showed recurring USB-C_plug wake events approximately every 13–15 seconds, sometimes accompanied by brief transitions from battery to AC power and charging sounds.

The same 140W adapter also works normally during overnight sleep tests when the charge limit is set to 80%.

There is another important symptom I should emphasize: When the battery is at 100% and the MacBook is connected to the 140W adapter, I can select Shut Down, the MacBook shuts down completely, but then powers itself back on without me touching anything. I have observed this behavior with the 140W adapter connected through both MagSafe and USB-C. I have not observed it with the Apple 20W adapter.

I wonder whether an intermittent power reconnection could be triggering the MacBook's automatic startup behavior, although I cannot confirm that this is the cause.

Given that the same MagSafe cable works without these recurring symptoms with the 20W and 35W adapters, I suspect the 140W adapter or its interaction with the MacBook's power management may be involved. However, I understand that this does not completely rule out the cable or the MacBook itself.

For now, I will continue using the 80% charge limit rather than replacing components without a clearer diagnosis.

Thank you again for your time and help.

kutz777 wrote:

MacBook Pro 16" M1 Pro (2021): repeated power connection events during sleep at 100% battery — Apple 140W adapter or firmware issue?

Hi everyone,

I'm trying to determine whether I'm dealing with a faulty Apple 140W power adapter, a macOS/firmware issue, or a hardware problem inside my MacBook.

I haven't been able to test another known-good high-wattage adapter yet.

Any experiences or suggestions would be appreciated. I'm particularly interested in whether others have observed the same behavior after recent software or firmware updates.

Did you just buy this Mac??? or it is an old issue...

Is this a replaced battery or OEM? Cycle count of 12 does not sound right as mentioned by Allan Jones.

Anywhere in there do you say what exact macOS you are running?

verify your software is up to date—The current stable release includes bug fixes.

Current Tahoe 26.7.2

Current Golden Gate 27.2 (edit: I see it now "macOS 27.2)

A SafeBoot https://support.apple.com/en-us/HT201262 will sort many anomalies

certain system caches get cleared and rebuilt—Reboot as normal and test. If this did not sort your issue I would get my hand on another magsafe and compare your results.

Try the user Diagnostic while you are plugged into your power source/troubled MagSafe...

may kick out an error code.

Use Apple Diagnostics to test your Mac for hardware issues

https://support.apple.com/en-us/HT202731

Best Buy has a generous return policy...

In or out of warranty you can get a free over the counter 'Apple Service Diagnostics' test /assessment

Make an appointment for a "hardware issue"

https://www.apple.com/retail/geniusbar/

Outside the USA

https://support.apple.com/en-us/HT201232

kutz777 wrote:

Thank you everyone for your replies.

Just to clarify a few points:

I purchased this MacBook Pro brand new in March 2026, although it is a 2021 model. As far as I know, the battery is original. I use the MacBook mainly connected to external power, which may help explain the low cycle count.

I have already tested Safe Mode, and the MagSafe issue still occurs there. Apple Diagnostics reported no errors.

I also tried replacing the removable AC wall plug on the 140W adapter, but that did not help.

The most interesting finding is that the repeated power-related events occur with my 140W adapter through both MagSafe and USB-C, while they were absent during comparable tests with 20W adapters.

I agree that testing another known-good Apple 140W adapter would be the most useful next step. Unfortunately, I don't have access to one yet.

I have also ordered an original Apple 35W adapter for an additional comparison.

Thanks again for your suggestions. I'll update the thread when I have more results.

You are still under the 1-yr warranty if purchased new. Why hesitate to get it resolved...Take it in let Apple tell you what is the issue.

The MagSafe charger is covered under the hardware warranty as well as the battery.

If the battery has sat unused for 5 yrs (2021) it could be the issue.

Not sure where you would even buy a "new" 2021 M1 (?) unless old inventory stuck on some shelf somewhere.

ref: https://checkcoverage.apple.com

kutz777 wrote:

Battery manufacturer: Sunwoda

That is one of the companies that Apple uses for its batteries. That sounds legitimate.

• Battery manufacture date: August 8, 2022

• Charge cycles: 12

• Full charge capacity: 8,667 mAh

• Design capacity: 8,694 mAh

• Battery health: 99.7%

• Battery temperature: approximately 24°C

Those are all good numbers for the battery. Typically the Mac manufacture date is several months after the battery date, so I'm guessing that your Mac dates from late 2022 (2021 models were produced and sold through 2023).

• Mac model: MacBookPro18,1 (16-inch, 2021, M1 Pro)

• Mac manufacture date: Unknown

As I said, I think your model was new in late 2022, or maybe early 2023. But I am mystified by why it would be kept in storage for 3+ years and then sold as "new."

I've attached screenshots of both information panels with the serial numbers hidden.

The battery appears to retain almost its full design capacity despite its age, although I understand this does not rule out all possible battery-related issues.

One particularly interesting result from my recent tests is that the MacBook remained asleep without any recurring power events for over nine hours at an 80% charge limit. After increasing the limit to 100%, without disconnecting the same 140W adapter, the MagSafe LED interruptions and charging sounds returned within 20 minutes.

Do these battery readings suggest anything concerning to you, especially considering the difference between 80% and 100%?

I feel that the simplest explanation is usually the most likely one. So one possibility is that the battery is somehow degraded due to 3+ years in storage (that is not good for lithium batteries) and that is causing what you saw. The other possibility is that the charger and/or its cable/AC-plug is somehow faulty.

I would try to get a new charger and AC cable, you can order them from Amazon, BestBuy, all kinds of sellers.

Meanwhile, I would simply use the Mac in the way you have discovered actually gets rid of that annoying symptom: set it to charge up to 80%. If I were doing this, I would use it like that for several months and then adjust the limit to 90%. If that works, then you can test to see if going to 100% is ok. Sometimes "exercising" the battery helps restore normal function at some level. Ideally you can eventually use it as Grant Bennet-Alder describes, allow the macOS to "manage" the battery charging level to optimize its lifetime.

The more complicated possibility is that there is some problem with your Mac hardware (or firmware) and that would be costly to figure out and fix. So I am hoping one of these simpler possibilities is what is going on and your workaround will enable a path forward.

I also realize you have limited service options at your location and probably were not offered a real warranty. But it might be that the above outlines a path forward that will work for you.

Hi,

You should take your MacBook Pro to your local retail AppleStore, Genius Bar or Apple Authorized Service Provider to check your MacBook Pro as well as AC Adapter there.

Thank you everyone for your replies.

Just to clarify a few points:

I purchased this MacBook Pro brand new in March 2026, although it is a 2021 model. As far as I know, the battery is original. I use the MacBook mainly connected to external power, which may help explain the low cycle count.

I have already tested Safe Mode, and the MagSafe issue still occurs there. Apple Diagnostics reported no errors.

I also tried replacing the removable AC wall plug on the 140W adapter, but that did not help.

The most interesting finding is that the repeated power-related events occur with my 140W adapter through both MagSafe and USB-C, while they were absent during comparable tests with 20W adapters.

I agree that testing another known-good Apple 140W adapter would be the most useful next step. Unfortunately, I don't have access to one yet.

I have also ordered an original Apple 35W adapter for an additional comparison.

Thanks again for your suggestions. I'll update the thread when I have more results.

I have a completely divergent opinion about your situation.

The symptom you complain about is that when the battery gets very close to 100 percent, the charger light starts to cycle, and likely it is doing very short charge cycles.

My recommendation:

DON'T DO THAT.

Enable battery health management feature and do not spend another moment of your time thinking about this.

Battery Health Management feature tracks your usage history and detects that you do not generally run your battery down to low levels. So when you see less than 100 percent as a full charge, it is charging less than the highest level for longest battery lifetime.

NOTE that charging to 80 percent is a side-effect, NOT the GOAL.

The goal is to have some hurly-burly (percolating activity) around using your battery, either by your actually using it, or by leaving it less than fully charged, so that the cells are not 100 percent charged 100 percent of the time. Battery Health Management will also from time-to-time let the battery decline slightly to 'get some exercise' and run lower (thought to be around twice monthly) if you do not do so by your ordinary use. It may also charge higher during this process.

The feature tracks your actual usage. If you continue to not require 100 percent charge for a few weeks, it generally will revert to a lower "full" level. but it takes some experience, which takes some time

If your recent usage patterns demand top battery capacity, the battery will charge completely to be sure you are not stuck out in the wild with no power.

Executive summary: “If you keep your Mac plugged in continuously for several weeks, it will start pausing the charge at 80%. If you run a small amount of the time on battery, it will keep doing that. If you run some of the time on battery, it will charge to 100%.” © 2025 neuroanatomist

<< ... before considering any expensive repairs. >>

[In my opinion] your Mac appears to be working as designed and simply does not need ANY repairs of any description.

That computer is a battery-CAPABLE device, It is not optimized as a battery-operated device (it is not an iPhone.)

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

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

In general, you should ALWAYS connect a power source when it is possible to do so, and only run on batteries (which could be somewhat slower) when no power sources are at hand. Modern Macs maintain optimum battery charge levels under program control, and will NEVER over-charge. Connected to Power is NOT necessarily charging.

When you set it down in one place, or set it down for the night, Plug it in. Then you won’t CARE whether it would drain the battery.

Kutz777 - I think if I were in your shoes I would be doing what you are doing. Although I would go for something more than 35W but that might be ok for what you are doing if it keeps the Mac from discharging overly.

By the way, if a laptop Mac is sitting shut down with its lid open, I believe the newer models will power on when connected to power. I think your power connection might be intermittently cutting out which could result in the Mac coming back on when the power connection is restored (e.g. the Mac thinks the MagSafe connection was pulled and reconnected).

It sounds like the 80% setting works ok for you (so far), so I guess 80% is the new 100% here!

Thank you for your help and suggestions!

I'm continuing to investigate the issue and perform additional tests. I'll share any significant findings in this thread.

I appreciate your time and assistance.

Hi steve626,

Thank you for your detailed reply and for suggesting coconutBattery.

I've installed coconutBattery 4 and checked both Battery Info and Mac Info.

Here are the results:

• Battery manufacturer: Sunwoda
• Battery manufacture date: August 8, 2022
• Charge cycles: 12
• Full charge capacity: 8,667 mAh
• Design capacity: 8,694 mAh
• Battery health: 99.7%
• Battery temperature: approximately 24°C
• Mac model: MacBookPro18,1 (16-inch, 2021, M1 Pro)
• Mac manufacture date: Unknown

I've attached screenshots of both information panels with the serial numbers hidden.

The battery appears to retain almost its full design capacity despite its age, although I understand this does not rule out all possible battery-related issues.

One particularly interesting result from my recent tests is that the MacBook remained asleep without any recurring power events for over nine hours at an 80% charge limit. After increasing the limit to 100%, without disconnecting the same 140W adapter, the MagSafe LED interruptions and charging sounds returned within 20 minutes.

Do these battery readings suggest anything concerning to you, especially considering the difference between 80% and 100%?

Thank you again for your help!

Hi steve626,

Thank you for taking the time to review the coconutBattery results and explain your thoughts.

I'm glad the battery readings appear normal, although I understand that calendar aging could still be a factor.

For now, I've returned to the 80% charge limit, where the MacBook remained stable during the overnight sleep test.

I have an original Apple 35W adapter on order and plan to use it for an additional comparison. I understand that this won't be equivalent to testing another 140W adapter.

I'm also still looking for an opportunity to test a known-good high-wattage Apple adapter before considering any expensive repairs.

I'll update the thread when I have more results. Thank you again for your help!

kutz777 wrote:

I understand that calendar aging could still be a factor.

Maybe, but if you have found a reasonable way to use what you have, it's ok!

For now, I've returned to the 80% charge limit, where the MacBook remained stable during the overnight sleep test.

Note that most laptops that are connected to chargers much of the time will be charged to 80% by Apple's automatic battery longevity algorithms. So 80% is fine. It would be nice to be able to charge it higher for times when you need to take it away to use running off its battery but you are figuring this out. Maybe you will be restricted to 80%, maybe not.

I have an original Apple 35W adapter on order and plan to use it for an additional comparison. I understand that this won't be equivalent to testing another 140W adapter.

I don't think a 35W charger is a good choice for your laptop. Your Mac comes with a 140W charger as standard equipment because Apple calculates that is what is needed when the computer is used under load. While a 35W charger may well slowly charge the laptop when it is powered off or asleep, when it is being actively used and under load it may not be able to keep up. I think Apple's 85W or 96W chargers could be used with your 16" MacBook Pro [I used those chargers with an M3 MacBook Pro 16" that had also came with a 140W charger and 85W and 96W seemed to keep up and charge my M3 even when it was under load] or MAYBE a 67W charger but with 35W I think it will lose charge even when connected to the charger if it is being actively used.

I'm also still looking for an opportunity to test a known-good high-wattage Apple adapter before considering any expensive repairs.

I still think either the battery is degraded in some way or the charger needs to be replaced (or its power cord). The ideal outcome I think here is that all you just need a new charger, but in that instance, 35W won't do, you would need something at least 85W.

Be careful who you allow to work on your Mac if you decide on repairs. You want a well qualified technician. I realize Apple does not have a presence in Russia where you are so your options may be limited.

I'll update the thread when I have more results. Thank you again for your help!

steve626 wrote:

I don't think a 35W charger is a good choice for your laptop. Your Mac comes with a 140W charger as standard equipment because Apple calculates that is what is needed when the computer is used under load. While a 35W charger may well slowly charge the laptop when it is powered off or asleep, when it is being actively used and under load it may not be able to keep up.

Yes. I use 140W via MagSafe charger with my MBP M5 16" while it is on a desk with its other peripherals (80% charge limit). But when on a couch I often use Apple's 20W charger via USB so I can prevent extra charging cycles. 20W keeps 80% in light use but the charge slowly drops if I use CPU intensive apps. While MBP sleeping, 20W can then charge to 80% quite fast.

Thank you for your reply.

I understand that macOS manages battery charging automatically and that keeping a MacBook connected to AC power is normal. My concern, however, is not simply that charging stops at 100%.

The issue is that, when my MacBook is asleep at 100% charge with the original Apple 140W adapter and MagSafe 3 cable, the green MagSafe LED repeatedly turns off and on, often accompanied by charging sounds.

The pmset logs show recurring USB-C_plug wake events approximately every 10–13 seconds, sometimes with brief transitions from AC power to battery and back.

There are two important findings from my recent tests:

• 140W adapter with an 80% charge limit: The MacBook remained asleep overnight for more than 9 hours without LED interruptions or charging sounds. The pmset log also showed no recurring power connection events. This stable behavior has been observed on multiple nights.
• 140W adapter at 100% charge: After increasing the charge limit to 100%, without disconnecting the adapter from the wall, the same issue returned within 20 minutes.
• 35W Apple dual USB-C adapter at 100% charge: Using the exact same MagSafe 3 cable, the MacBook remained asleep for approximately 23 minutes without the recurring power events seen with the 140W adapter.

I understand that the 35W adapter is not suitable as a full replacement for the 140W adapter under load. It was used only as a comparison.

These results suggest that the behavior depends on both the battery charge state and the power adapter being used.

Could this indicate a problem with the 140W adapter or its USB Power Delivery negotiation with the MacBook, rather than normal battery management?

Thank you for your help!

<< The issue is that, when my MacBook is asleep at 100% charge with the original Apple 140W adapter and MagSafe 3 cable, the green MagSafe LED repeatedly turns off and on, often accompanied by charging sounds.

The pmset logs show recurring USB-C_plug wake events approximately every 10–13 seconds, sometimes with brief transitions from AC power to battery and back.>>

For longest battery lifetimes, your Mac should not be kept at 100 percent charged state.

So symptoms you see ONLY at that state are not important, and not actionable.

You do not have a problem.

Thank you for your reply. I understand that keeping the battery at 100% for extended periods is not ideal.

However, this is not just about internal power management events. When my MacBook is asleep at 100% with the Apple 140W adapter, the MagSafe LED repeatedly turns off and on, accompanied by charging sounds and the battery/charging indicator appearing on the screen.

This happens approximately every 10–13 seconds. With the same MagSafe cable and an Apple 35W adapter, these symptoms do not occur.

I find it difficult to consider repeated audible and visible charging notifications during sleep normal behavior, even at 100% battery charge.