Clamshell Mode - Battery Drop when Disconnected

[chefwong]

I have my MBP set to charge to 90% . It's generally in clamshell mode
If I disconnect it for travel, without usage, I see it has dropped to 80% .

I'm clear all batteries need to be -cycled, excercised- to be healthy.
Would we say the OSX is draining the battery when it's disconnected in order to cycle-calibrate the battery as needed

-Alan

 

[benholt]

Couple of things stacked here rather than a calibration cycle. With the 90% cap set, the pack self-discharges from 100 down toward 90 rather than being trickle-charged back up, so if it's been plugged in for a while the real state of charge is already drifting a few points below the 90 you see displayed. Unplug and the true reading unmasks.

Then even a sealed clamshell sleep has some background activity — iCloud sync, Bluetooth peripheral polling, Power Nap tasks. 24 hours of that easily shaves another 3–5% on top of whatever drift was already there.

Apple Silicon doesn't really do a hardware calibration cycle the way old Intel MBPs did, the fuel gauge is software-modeled continuously. System Settings > Battery > Battery Health > (i) shows cycle count and max capacity if you want to sanity-check the pack itself.

 

[chefwong]

Thanks Ben. So in sleep mode. even with TB cable plugged in, intake is on battery and it's only taking a charge when out of sleep as well ?

 

[benholt]

Right — when the lid is closed and the system is in sleep, the port stops charging as soon as sleep is fully committed. Thunderbolt still keeps a trickle running the SMC and lets peripherals wake the Mac, but the pack itself isn't being topped up. Anything the Mac does in that state (Power Nap wakes, Bluetooth polling, iCloud checks) pulls from the battery instead of the wall.
When you wake it or open the lid, the charger kicks back in and the battery starts absorbing again. You can watch it in Activity Monitor > Energy or in System Settings > Battery > History. If you want the pack to actually keep topping up under a closed lid, disable Power Nap in System Settings > Battery > Options. Won't help on a warm afternoon in clamshell with a full setup running, but it's cleaner than the default.

 

[ignatius345]

I have an older relative who keeps her MacBook Air plugged in 24/7/365. When I remote in to help her with stuff, I see the message above. The charging system will start limiting the charge to 80% if you leave it plugged in a lot. Not sure what the threshold is for that. Are you seeing this message when you’ve had it in clamshell mode for a while?

When she replaced her last MacBook after like 6 years, there were like 5 battery cycles on it, and all those were from when I’d come visit and unplug the poor thing for a few days 🤣