Macbook pro clamshell mode done wrong

[JulesQper]

I guess I used clamshell mode wrong for over 3 year....

I use my 16" intel MBP (2019) in clamshell mode for over 3 years now. I am really happy with my workflow since I manly use the mac as a desktop for heavy tasks and take it out at a maximum of 1 time each month. I use my iPad pro as my daily device for on the go so thats why my mac is constantly at my office. Just to complete the setup, I have connected one USB C for power, one USB C to HDMI for my 34" monitor and one USB C extension where I plug in a variety of cable's/adapters when needed. For controlling the mac I use a Magic keyboard and trackpad.

For the last 3 years I used my setup like this: I turned on a power brick with the monitor and the mac's power adapter attached to it to turn on power on these 2 devices. When the day was done I would turn the power brick off and all of the devices would be powerless. The idea behind this is that there wouldn't be any standby power and the mac would go to sleep so there wouldn't be any power consumption (at least I taught so). p.s. I don't put the mac in sleep or anything I assume(d) it would go to sleep by itself since there wouldn't be any power to it anymore.

Since a couple of weeks I noticed the following: While working on the mac it would charge to its full 100%. After I turn off the power brick and leve everything unattended the mac would start the next morning with a percentage of 50-70% depending on how long I left it unattended. I discovered with help of istats menu that even the CPU was long active after turning off the power and therefore drained the power.

After some research I found that most clamshell users leave their MBP connected to the power at all times, and got some questions:
Is leaving the power on at all times the right way to do it? So only turn off the power of the display? Does the macbook go to sleep then by itself or do you all put the mac to sleep? In my opinion it can't be good to keep a mac awake 24/7, or am I wrong?

 

[mystery hill]

I don’t turn anything off.

The external display will go to sleep automatically after being inactive for some time.

 

[ahmedfarhan]

Yeah, it’s better to leave your MacBook plugged in while in clamshell mode, just put it to sleep or let it auto sleep when not in use, since cutting power completely can prevent proper sleep and cause the battery to drain overnight.

 

[JulesQper]

Allright, thanks for the feedback so far. Only thing I can't figure out is how the mac should go to sleep automatically. Even when the power supply is turned off the mac stays on for about 6 hours or so. I would suspect that when all power is off it should go to sleep almost directly.

 

[BigMcGuire]

Leaving a Mac on 24/7 isn't a bad thing. I usually do CMD+CTRL+Q and then ESC to force sleep as I walk away from my desk. (Sometimes I accidentally hit the mouse and wake it back up as I'm walking around - and have to do the CMD+CTRL+Q and ESC to put it back to sleep).

In the settings - you can have "Prevent automatic sleeping on power adapter when the display is off" - make sure this is off if you want it to sleep.

"Wake for Network Access" -- I usually have Only on Power Adapter.

And yeah, in my experience, the moment I pull the power - it goes to sleep right away.

 

[JulesQper]

CMD+CTRL+Q and then ESC

I know this trick and did that sometimes a long time ago when I left my mac unattended. I made hotcorners to go to lock screen and with the press of esc everything went dark. But since the update to macOS26 esc doesn't turn my lock screen off anymore.
Therefore that is not a way to put my mac to sleep anymore.

But is there no way to change settings or something to have a clamshell MBP go to sleep after a pre set time? I'm allmost sure that this was possible in older OS.

 

[BigMcGuire]

I know this trick and did that sometimes a long time ago when I left my mac unattended. I made hotcorners to go to lock screen and with the press of esc everything went dark. But since the update to macOS26 esc doesn't turn my lock screen off anymore.
Therefore that is not a way to put my mac to sleep anymore.

But is there no way to change settings or something to have a clamshell MBP go to sleep after a pre set time? I'm allmost sure that this was possible in older OS.

Yeah I remember this setting too - I think the closest thing now is:

Lockscreen:

 

[JulesQper]

Okay thank you I got the sleeping to work I guess and put the mac to sleep for 2 hours. After turning back on the mac I checked the CPU processes of the last hour (iStats menu) and saw that the CPU woke up every 5 minutes or so. Is it then actually in sleep or not? I would assume in sleep there will be no activity.

 

[BigMcGuire]

Okay thank you I got the sleeping to work I guess and put the mac to sleep for 2 hours. After turning back on the mac I checked the CPU processes of the last hour (iStats menu) and saw that the CPU woke up every 5 minutes or so. Is it then actually in sleep or not? I would assume in sleep there will be no activity.

If plugged in most Mac’s will wake up all the time to keep mail and iMessages updated. Perfectly normal. At least on my Mac it is. Lol

However unplugged, should be no activity.

 

[JulesQper]

So to make a conclusion.

Clamshell mode is best to use with power always connected. The mac will get its rest in sleep and the waking up of it in between is no problem for the machine.
When there is no constant power connection when the mac is put at sleep, the mac will drain battery overnight and charging back the day after. This is what I did for the past 3 years but was a bad idea seems so. My cycle count is 495 and health is at 86%.

So in the future if I buy a new MBP and use it in clamshell mode it's best to leave it to constant power and let the mac handle itself.

 

[BigMcGuire]

Yeah that's what I do. I leave my Mac connected to power 99.999% of its life - clamshell to a monitor.