Strange external monitor behavior

[sturg]

So I want to use my new, M1 Pro, MBP with an external monitor. And I want to use it with the computer lid/screen closed, in clamshell mode. So I hooked up my brand new LG monitor today, and it works fine as long as I have the computer charging cable plugged into the computer. As soon as I disconnect the charger cable from the computer the monitor screen goes black and says no signal. I figured that there's gotta be a setting on monitor or on the computer that I can adjust to change this behavior.
First I called LG, but they said to call Apple, which I did. The senior tech advisor from Apple told me that there is nothing to change on the laptop and this is EXACTLY how the computer and monitor is supposed to behave. He said that there is nothing to worry about as far as having the computer plugged and constantly charging 24/7. He said no harm will come to the battery or the charger or the computer from doing this. He said the reason that the monitor turns off when disconnected is because the computer does not have enough power to run the monitor without being plugged in......BUT isn't that what the power plug on the MONITOR is for?? To power the monitor?
What have been your experiences with this issue? Does this seems right?
I just can't get used to leaving that charger plugged in all the time.
Any advice is much appreciated. Ty.

 

[MacInWin]

My M1 MBP is plugged in pretty much 100% of the time. In System Preferences/Battery, I have selected "Optimized battery charging." The charging circuit is "smart" in that it will recognize that you don't use it on battery very often and will slowly let the charge decrease to about 80%. The charger light will change from green to orange to show that it's not fully charged. You can click on the battery icon and it will report that it is operating in this mode. Here is a screenshot from mine:



If I take it off the power and use the battery for a bit, it reverts to "normal" and charges back to 100%, but in a few days re-learns that it's rarely used on battery and lets it decline again.

So, why 80%? Well, lithium batteries like to be in the range of 60-80% for optimum life overall, so 80% is a good place to be, and it can charge back to 100% very quickly from there.

So, leave it plugged in all the time and let it learn.

Yes, it's a new behavior, but it works!

I also have my Battery settings in System Preferences set to keep the CPU ticking over and the drives active while the screen is dark from inactivity. The current used is minuscule, and the system wakes immediately with one press on the space bar, which is very nice.

Here are my settings:







So, the advice you were given was correct. Keep it on mains power, let optimization do its thing and the monitor should work.

 

[ferrarr]

I just can't get used to leaving that charger plugged in all the time.

If you need to unplug the MBP, go for a walk to the living room with it.

 

[krs]

So, the advice you were given was correct.

Including this part?

He said the reason that the monitor turns off when disconnected is because the computer does not have enough power to run the monitor without being plugged in.....

Is the LG monitor really powered over one of the two TB ports?

If one port is used to connect the LG monitor and if the other TB port must be used at all times to power the Mac when a monitor is connected, that leaves exactly zero TB ports for anything else.
Well.... unless one spends more money for an external box.

I'm not questioning that the system actually works that way, the "reason" just doesn't make sense.

 

[MacInWin]

Is the LG monitor really powered over one of the two TB ports?

Probably not. I've not heard of any monitor powered from the computer that way. I have no idea why the tech guy said that. And it doesn't work that way on my MBP. My external monitor has it's own power and works just fine when on battery.

 

[Randy B. Singer]

Including this part?

Is the LG monitor really powered over one of the two TB ports?

I'm not questioning that the system actually works that way, the "reason" just doesn't make sense.

I've never heard of a monitor that requires that your MBP be plugged-in to the AC adapter for it to work. I don't use any of my laptops as desktops currently, but I have in the past, and none of them worked that way. If I were in your situation, I'd return the monitor and get a different one.