I have Asperger's, so this might just be me not understanding how the 'battery optimisation' feature is supposed to work (it's currently not turned on - according to Settings > Battery > Battery it's switched off until 06:00).

This is making me nervous; at the moment, the computer is never used on battery (my current situation means I can leave it connected 24/7) yet the battery still drains and I have to 'charge to full now' about 4 or 5 times a day. Is this expected behaviour? Why would the battery discharge when it's connected to mains power? I'm using the supplied 140W charger and MagSafe cable, and it's plugged directly into the wall socket, no adapters.

I had a similar issue with my iPads (2017 and 2020 Pros) but, in that case it was because there was a mismatch between the charger and the cable (ie the cable was drawing current faster than the charger could supply it which caused the batteries to drain. Once I bought a more powerful charger, the problem resolved itself).

Obviously, this shouldn't be the case here - should I be having a word with Apple about this? Looking at the battery indicator and seeing it on 72% when it's not been unplugged is somewhat unnerving (this laptop was an early Xmas present from my parents to replace my loathed 2016 Touch Bar).

Unfortunately, despite the nearest Apple Store being just over 3 miles away, ill-health prevents me from making a Genius Bar appointment (should it be warranted). I have AppleCare+ to the end of 2024.

Apologies for what is, probably, another stupid question.

Happy whatever it is you may celebrate (or not)


  • The system is trying to prolong your battery's life - you're trying to shorten it by insisting it should always be fully charged. Let the Mac handle it, it does it better than a human can.
    – Tetsujin
    Commented Dec 26, 2021 at 8:41
  • I also started having the same issue from past two days. My M1 Max battery is also draining when it's plugged in. I contacted Apple support, they told me to reload the machine in safe mode, etc but these hacks generally never work. So, I'm keeping the Mac plugged in and see what it does when it goes around say 50-60%.
    – CopsOnRoad
    Commented Dec 27, 2021 at 22:45
  • 1
    How low is it getting? Unless it's going below 50% or whatever then yes it's expected.
    – Ezekiel
    Commented Jan 27, 2022 at 23:50
  • This is not intended and likely a bug. I have tested the 16" M1 Pro against the 16" M1 Max, both with optimized battery charging enabled. The issue is only present on the M1 Max machine. Lithium ion batteries self-discharge at a rate of 1-2% per month. In my testing, the M1 Max battery dropped about 5% in about an hour while plugged in, while doing light web browsing. This suggests that the machine is drawing power from the battery and not AC power as it indicates.
    – Bren
    Commented Feb 26, 2022 at 2:55

1 Answer 1


Short answer: No, you shouldn't be worried about it as it is because of the Battery Optimization that knows how to handle your charging i.e. when to charge/discharge your mac.

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I kept my new mac plugged-in at all times. For 10-12 days, it used to show full 100% charge but recently it started discharging while plugged in. I was also worried about this, but then I found that the charge didn't go below 80%, that means the machine was learning from my charging routine, how I am charging my mac. Once it has gained sufficient data, it knows that I always keep it plugged in, so it will not charge past 80% to prolong battery's life, you can find more information here

If you use optimized battery charging in macOS Big Sur or later, or use macOS Catalina or earlier, occasionally the battery might not show a full charge (100%) in macOS, even after the power adapter has been connected for an extended period of time. This behavior is normal and helps prolong the overall life of the battery.

  • 1
    I'm still seeing this behavior even after disabling "Optimized battery charging", which seems wrong. I just contacted Apple support about it, and they suggested I send it in for repair.
    – Greg Brown
    Commented Mar 17, 2022 at 19:45

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