MacBook Pro 16" with LG 24" - not charging

A notebook Mac uses up to the entire output of the power adapter. If more is needed for intensive computation and processing, it freely "borrows" power from the battery. It does this on a moment by moment basis, and it generally is does not show you that this is happening. When you ask that particular high-powered notebook Computer to do graphics intensive operations, It may appear that the charge level on the battery is going down. That is because it IS going down.

Your computer is working as designed. If it did not "borrow" from the battery, the power adapter would have to be MUCH larger, or your ability to do computations would be severely throttled.

If you then proceed to use a power adapter (the one in the display) as the ONLY power adapter, and it provides LESS that the required capacity for the computer, unexpected things can happen. Apple recommends you use a power adapter rated at least as high as the original power adapter specified for the machine. Nothing else is considered acceptable.

In some cases, using a too-small power adapter will appear to work, but will draw down battery power very rapidly.

In extreme cases, your Mac could over-draw the available power. Over-drawing the available power will result in an emergency, uncontrolled power-down, as your Mac takes steps to save itself from damage.

The recommendation has always been, and continues to be, to connect a power adapter of at least the minimum specified for your computer. Apple does not provide any guidance for connecting multiple adapters, but Users report it works.

Find the right power adapter and cable for your Mac notebook - Apple Support

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Hey,

Do you have any USB-C stuff plugged to the display? After a chat with Apple Support, I tried to unplug everything I had connected to the display (keyboard, trackpad and backup disk through all necessary dongles) and it seems to charge that way. When I start plugging stuff in, it stops charging. I still have to do some more tests to be sure this is not a red herring, but let us know if you have stuff plugged to the display and if unplugging changes the behaviour. Note that when it stops charging, I have to unplug everything, unplug the Mac from the display itself, wait a few minutes for the display to reset, and then plug the Mac to the display again. It always takes a little bit for the Mac to start charging, so give it some time when testing.

Regards,

Miguel Arroz

Same experience here. The LG 24" will charge the MBP 16" as long as the processor usage is low and the machine is in clamshell mode. With significant power usage (high processor use, screen open), the battery will drain.

In my case with a MBP 16" and LG5k27", the culprit was Parallels. Quitting Parallels allowed the battery to charge and the fan to stop running constantly. So I guess I have to avoid using Parallels unless there is a firmware upgrade or MBP update that fixes the issue - seems like bad design to limit open apps or force using a separate power adapter.

As one more data point - after my post above, I experienced the issue once again, while Photos was updating a large library. I had the same experience as Mattias - even after shutting down the intensive processes, the MBP did not resume charging. The lighting sign did not return to the menu bar, and the battery percentage kept dropping. Activity monitor confirmed that there were no processes using significant energy. Only a hard reboot restored charging functionality through the LG display. I agree that it sounds like a bug somewhere - apparently, once the machine starts draining the battery because the charging power of the display is insufficient, it does not resume charging even after the power-hungry processes are no longer running.

(Edit - posted at the same time as Miguel above. It appears to be a very similar phenomenon. Must unplug everything / reboot for the MBP to resume charging).

I think I might have solved the problem in my case. As well as intermittent failure to receive power from the LG, I was also having real issues getting my 16” to see any USB peripherals connected via it, and I eventually discovered that it was because of the LaunchAgent for a particular audio interface (the Arturia AudioFuse). Removing this solved the problem completely, and although I’ve not tested extensively, the 16” also appears to get power correctly now. That particular issue was intermittent for me, though, so it may or may not have actually been solved.

So, it seems that certain connectivity LaunchAgents can affect the working of the LG. Might be worth trying to move any on your system out of the LaunchAgents folder and rebooting to see if that helps, then replacing them one by one to narrow it down. I figured this all out when I realised that the LG worked perfectly when the Mac was in in Safe Mode (ie, with no non-Apple LaunchAgents running).

to be clear, like you I had no issues whatsoever with any other Mac and the LG – this was only happening with the 16” MBP.

I had this happen too the first time I tried it, but then, after disconnecting and reconnecting everything connected to the LG and restarting the MBP (I'd imagine the latter was the one that actually made a difference), it seems to work okay. The battery still drains and charges constantly, depending on workload, and it doesn't feel ideal, but Coconut Battery is now showing power as 'connected', which it definitely wasn't on my first try.

It's probably too much to expect a firmware upgrade from LG to increase the wattage the monitor passes through, sadly. :(

Hi,

I'm having the same issue, only difference is I have the LG 5K display. Sometimes it charges without issues (and rather quickly), others it drains also pretty quickly. This doesn't seem related to the workload on the Mac, as it will drain even when the Mac is asleep (or at least the screens turned off), or when I'm using it but with CPUs mostly idling. It seems completely arbitrary. Yesterday I filed an FB on this. The battery was draining, when it got to less than 20%, I rebooted the Mac, power cycled the display, and it still didn't fix it. While I was writing the FB, it started working by itself and charged in less than 3 hours.

This seems like a bug. Even if the LG doesn't provide as much power as the charger, the fact it switches from draining to charging arbitrarily (and charging quickly, not taking the entire day) points in the direction it's not just a lack of power issue.

Regards,

Miguel Arroz

Funny. I too have the 16" MBP running to the LG 5k2k 34" monitor (LG 34WK95U-W 34") and started experiencing this issue tonight. I've ran it for about 2 weeks with no issues and then today it would not charge. I rebooted both to no success (it was dying while not even being used). Finally I changed port and it seemed to fix the issue but agree with the above post. Seems to be some bugs in the setup and given the array of screens here (though all LG) I would assume it to be a bug with the 16" MBP.

What is your configuration and when did you buy it? What wire do you use to connect to the monitor?

MBP will pull however much power is needed to charge. If the pulled-source cannot handle it, bad things can happen. From "not charging" to "burns out the pulled-source".

Every hour you spend trying to make a non-working solution actually work is an hour of your life you can never gat back.

How much is the power consumption of your external monitor? And when you connect an external monitor, your GPU 5300 starts working?

Hi, when you connect an external monitor, you do not notice the noise of the fans, can you tell what the speed of the fans when you work (PHPStorm, Visual Studio Code, GirKraken, Chrome, mysql database tools and Slack)? I have a problem with heating and noisy fans when connecting an external monitor https://discussions.apple.com/thread/250878229 and I don't know what to do with it =(