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I've recently got a big screen "dell U3421WE". It works great as I can finally save a charger and charging cable. It's all because this display can provide you the power. In the official specs it says:

your monitor serves as a productivity hub that delivers stable Etherneti and up to 90W of power delivery—all in a clutter-free setup.

But it's weird that since using this feature and removing my original charger. I noticed that my battery has never reached 100%. For instance:

enter image description here

I have never removed the USB-C cable between my display and MBP, so it's always charging.

Is there anything wrong? Should I put back the original 96W Apple charger?

Updates:

I noticed that my display's power is 90W and the Mac's official charger is 96W. Is that a problem I should take care of?

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The answer is right there in your screenshot:

Charging On Hold (Rarely Used On Battery)

It does this because holding a full charge of 100% tends to stress the battery. By keeping it a bit lower, it prolongs the battery's useful life.

You can turn off this behaviour in Settings -> Battery -> Battery.

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  • Thanks, I have updated my question. Jul 5, 2021 at 5:40
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Is there anything wrong?

No.

The explanation for the behaviour you are observing lies in the following Apple support document:

If battery charging is paused or on hold on your Mac

With macOS Big Sur, your Mac learns from your charging habits to improve the lifespan of your battery.

In macOS Big Sur, Optimized Battery Charging is designed to improve the lifespan of your battery and reduce the time your Mac spends fully charged. When the feature is enabled, your Mac will delay charging past 80% in certain situations. Your Mac learns your charging routine and aims to ensure that your Mac is fully charged when unplugged.

You likely have Optimized battery charging enabled under System Preferences → Battery → Battery

enter image description here

As you have already mentioned that you keep your MacBook plugged-in all the time, with the aforementioned setting enabled, your Mac is waiting to finish charging past 80% to optimize battery aging.

To disbale this behavior and keeping the battery charged to 100%, you can uncheck Optimized battery charging.

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  • Thanks, may I ask that whether the 90W vs 96W should be an issue to put into consideration? Jul 5, 2021 at 5:40
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    It should not be an issue.
    – Nimesh Neema
    Jul 5, 2021 at 5:42
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I noticed that my display's power is 90W and the Mac's official charger is 96W. Is that a problem I should take care of?

It's only a problem if it means your Mac goes into a power save mode due to a low battery sate, this from having to draw from the battery to keep up with power demands. Seeing that your activity has lead the battery optimization to not fill the battery to 100% would lead me to believe that your display is providing sufficient power for your average needs.

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  • It this the reason sometimes I feel my Mac is not very fast? But it’s weird that even if at the morning of a new day, with a whole night relax, the battery still shows 80% Jul 17, 2021 at 0:56
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    " It this the reason sometimes I feel my Mac is not very fast? " Not likely. If the operating system sees that there is a high load necessitating the use of battery power consistently to keep up with power draw then it would not optimize the battery charging to keep the battery charge level to only 80%. If this concerns you then there is no harm in connecting the Apple 96W charger, except perhaps losing a much needed USB-C port for some other accessory. Even that can be resolved with any of a number of docks or hubs to add ports with minimal costs.
    – MacGuffin
    Jul 17, 2021 at 2:29

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