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User profile for user: DelegatorNH
DelegatorNH Author
User level: Level 1
24 points

16 Inch MacBook Pro Battery Drains under load even when plugged in

I have had this problem with two successive 16-inch MBPs now. Using the 96W power adapter and cable that come with the machine, when under heavy load the battery loses 1% of its charge about every 1-2 minutes, and then of course shuts down when it reaches 0%. This was confirmed by the Apple Store techs under Full System Diagnostics, and I received a replacement machine, but this shows the same behavior.


When I look at the System Report under About This Mac, it shows that the power adapter is drawing just 60W even though it is recognized as a 96W adapter:


This has been consistent with all three of the Apple brand power adapters that I bought (one for home, one for the office, one for travel.


The reason I ended up with a second machine is that the repair center claimed they couldn't reproduce the problem (even though the Apple Store reproduced it both times) likely because they just saw the system as charging and didn't put it under heavy enough load. I was dismayed, to say the least, to see this new system exhibiting the same problem. And of course I had reset the SMC, reinstalled the OS, etc., etc., etc. before even sending it out for repair and losing use of the system for a week.


Is this expected behavior? Because if it is, then I need to return this machine for a refund and stick with my 2015 MBP that can actually retain a charge under load. Otherwise, what's the fix?

MacBook Pro 16", macOS 10.15

Posted on Feb 2, 2020 3:01 PM

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User profile for user: DelegatorNH
DelegatorNH Author
User level: Level 1
24 points

Posted on Feb 3, 2020 1:10 PM

Believe me, I know how frustrating it is. Here are my suggestions.


First, Go to "About this Mac" -> "System Report" -> Power and scroll down to AC Charger information. If you are plugged directly into power (e.g. not through a port replicator) it should look like this:

but with a substandard cable might see this (which is what I had)

Note the wattage coming in is only 60W despite the power adapter being correctly identified. Now with the right cable, even with a port replicator you might not be getting full power delivery (despite being rated at 100w) I get this

and the 84w is enough to keep my system charged even under intense load where the 60w was not. And the Mac can't identify the power source like it can with the Apple adapter.


Then, if you are seeing low wattage delivered, check the cable serial number according to this article:


https://support.apple.com/en-us/HT201700


  • If the first three characters of the serial number are C4M or FL4, the cable is for use with the Apple 29W or 30W USB-C Power Adapter.
  • If the first three characters of the serial number are DLC, CTC, FTL, or G0J, the cable is for use with a USB-C Power Adapter of any wattage.


Now, finding the serial number is harder than you'd think because the text is basically grey on a light grey/white cable. On mine it was about 6 inches from one end of the cable, on the side, not what you would think of as the top or bottom when plugged in (of course there are two ends to look at, and two aides on each end). And it looks like this:



As you can see, you'll need a bright light and some good eyes to see it. Check the serial number against the note above.


Hopefully that will help a bit.

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User profile for user: DelegatorNH
DelegatorNH Author
User level: Level 1
24 points

Feb 3, 2020 1:10 PM in response to Chrisrobertsnyc

Believe me, I know how frustrating it is. Here are my suggestions.


First, Go to "About this Mac" -> "System Report" -> Power and scroll down to AC Charger information. If you are plugged directly into power (e.g. not through a port replicator) it should look like this:

but with a substandard cable might see this (which is what I had)

Note the wattage coming in is only 60W despite the power adapter being correctly identified. Now with the right cable, even with a port replicator you might not be getting full power delivery (despite being rated at 100w) I get this

and the 84w is enough to keep my system charged even under intense load where the 60w was not. And the Mac can't identify the power source like it can with the Apple adapter.


Then, if you are seeing low wattage delivered, check the cable serial number according to this article:


https://support.apple.com/en-us/HT201700


  • If the first three characters of the serial number are C4M or FL4, the cable is for use with the Apple 29W or 30W USB-C Power Adapter.
  • If the first three characters of the serial number are DLC, CTC, FTL, or G0J, the cable is for use with a USB-C Power Adapter of any wattage.


Now, finding the serial number is harder than you'd think because the text is basically grey on a light grey/white cable. On mine it was about 6 inches from one end of the cable, on the side, not what you would think of as the top or bottom when plugged in (of course there are two ends to look at, and two aides on each end). And it looks like this:



As you can see, you'll need a bright light and some good eyes to see it. Check the serial number against the note above.


Hopefully that will help a bit.

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User profile for user: Kappy
Kappy
User level: Level 10
361,849 points

Feb 2, 2020 8:32 PM in response to DelegatorNH

You have a machine under warranty. We can do nothing to help you resolve your issue with Apple or the Apple Store from which it was purchased. You will have to use your warranty. If you feel you wish to speak directly to Apple, then you can contact Apple Support.


Contacting Apple Customer and Support Service


  1. Apple Store Customer Service at 1-800-676-2775 or visit online Help for more information.
  2. Primary support help at Contact Support.
  3. To contact product and tech support:  Contacting Apple for support and service including international calling numbers.


FYI: These are user-only forums. You are not speaking to Apple. if you need to speak with Apple Support, then contact product and tech support:  Contacting Apple for support and service including international calling numbers.


Thank you for your understanding and support.

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User profile for user: DelegatorNH
DelegatorNH Author
User level: Level 1
24 points

Feb 2, 2020 8:43 PM in response to Kappy

Well as I said I already had the machine sent for repair and they said they couldn't reproduce the issue, then when the store reproduced it they replaced it and the new machine did the same thing. But I guess I will go through the whole support process again (sigh) and just return the machine if this is determined to be normal behavior. Funny how my 2015 MBP doesn't have this issue.

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User profile for user: Kappy
Kappy
User level: Level 10
361,849 points

Feb 2, 2020 8:47 PM in response to DelegatorNH

The behavior is not normal under known conditions, but we have no way to test your machine. Only the techs have the equipment needed. It's possible the battery is in use when not using the AC adaptor by some running process that is causing the battery's power to decline. I'm sorry but we don't intend to be disappointing but we cannot do much with hardware related problems.

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User profile for user: DelegatorNH
DelegatorNH Author
User level: Level 1
24 points

Feb 3, 2020 8:02 AM in response to Kappy

Looks like it is a problem with the USB-C charging cables I bought. Because the Apple 96w power supply doesn’t come with a cable I had purchased ones off Amazon which turned out to look exactly the same but not deliver more that 60w where the Apple one shows as delivering 94w. I had to check the serial number based on the support note about identifying the right cable. Burned by counterfeits, probably not the only one.

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User profile for user: Chrisrobertsnyc
Chrisrobertsnyc
User level: Level 1
18 points

Feb 3, 2020 10:55 AM in response to DelegatorNH

Hi I am having exactly the same problem. I exchanged the first 16” MacBook pro for a new one and the problem persists, it happens when I am running video processing applications (that I used to run on a 2015 13” MacBook Pro without problem!) and the machine is under somewhat heavy load, but only some of the cpu is in use while the gpu is under heavy load. The computer slowly drains until it dies. I am using the Apple 96w charger and cable. It’s really disappointing to have spent this much and the computer can’t power itself.

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16 Inch MacBook Pro Battery Drains under load even when plugged in

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