Here's why you should probably charge your MacBook Pro using the ports on its right side

By Oliver Haslam
last updated

MacBooks from the back
MacBooks from the back (Image credit: iMore)

What you need to know

  • MacBook Pro notebooks charge via USB-C.
  • You can charge using ports on the left or right.
  • But using the one on the left could cause high CPU usage because reasons.

If you're using a new-ish MacBook Pro you're probably enjoying the fact that you can charge using the USB-C ports on either side of your notebook. It's a small thing, but it can make a big difference depending on where your charger is plugged into the wall. But it turns out that while charging from either side does work, you might want to charge using the ports on the right from now on.

That's because some people charging using the ports on the left side of their computer have also noticed unusually high CPU usage thanks to a process called kernel_task. As noted by one StackExchange user, their Mac would spin up the fans and become unusable when this happened. They even shared a screenshot of the kernel_task going to town.

Screenshot showing Activity Monitor and high cpu usage

Screenshot showing Activity Monitor and high cpu usage (Image credit: "Adam")

But I know you're asking the obvious question – what's this got to do with charging? It's a good question and one that was answered emphatically in the same thread.

I'm not going to get into all the nitty-gritty of what's going on – you can read Adam's post for that – but the tl;dr is pretty simple. When you're charging using the left-hand ports and have other accessories plugged into the same side, things get a bit too warm. So warm that the Thunderbolt Left Proximity sensor sees the increase in temperature and the kernal_task process appears. It's game over at that point with fans spinning up and CPU usage skyrocketing. Over to Adam for his testing method:

State A a USB-C hub (a mouse and keyboard, plus power) and a USB-C HDMI 2.0 adapter, both on the left side. You can see the Thunderbolt Left Proximity temperature sensor rise quickly. About 3-4 minutes later the dreaded kernel_task high CPU usage starts.State B cures the kernel_task problem by moving power from the left ports to the right. The left side temperature drops and the kernel_task goes away within about 15 seconds.This is causal. Moving power back to the left side, restoring State A, quickly restores the temperatures and kernel_task again comes back after 3-4 minutes. Again moving power back to the right side, restoring State B, resolves the problem immediately.

Amazingly, this is actually a thing that happens. And there are others in the same StackExchange thread sharing their own experiences with the problem and the fix. So here we are – if you're charging your MacBook Pro, and particularly if you have accessories plugged in, use the ports on the right.

Who knew?

Oliver Haslam
Oliver Haslam
Contributor

Oliver Haslam has written about Apple and the wider technology business for more than a decade with bylines on How-To Geek, PC Mag, iDownloadBlog, and many more. He has also been published in print for Macworld, including cover stories. At iMore, Oliver is involved in daily news coverage and, not being short of opinions, has been known to 'explain' those thoughts in more detail, too.

Having grown up using PCs and spending far too much money on graphics card and flashy RAM, Oliver switched to the Mac with a G5 iMac and hasn't looked back. Since then he's seen the growth of the smartphone world, backed by iPhone, and new product categories come and go. Current expertise includes iOS, macOS, streaming services, and pretty much anything that has a battery or plugs into a wall. Oliver also covers mobile gaming for iMore, with Apple Arcade a particular focus. He's been gaming since the Atari 2600 days and still struggles to comprehend the fact he can play console quality titles on his pocket computer.

5 Comments
  • What if your peripherals and power are on the right? Perhaps it is best to say you should split up the tasks to overheating. Power on the right and peripherals on the left or Power on the left and peripherals on the right. Have you tried that?
  • I cannot replicate this. I have both the 13 inch MacBook Air 2018, and the 16 Inch MacBook Pro from 2020.
  • Hi Mr. Trebek, I'll take "Shotgun QA" for 500...what's that? It's the year 2020 and Apple no longer tests new features or security vulnerabilities after patching, with their end-user base? Noice, straight capitalism at its greediest. supportDOTappleDOTcom/guide/apple-configurator-2/revive-or-restore-mac-firmware-apdebea5be51/mac
  • The 2016/17 13" Touch Bar do have a difference between the left and right USB-C ports with their throughput related to the PCIe lanes they use. The power services are the same for each side. The same Intel JHL6540 Thunderbolt 3 Controller chip per each side. The 2016/17/18/19 15" Touch Bar models use the same Intel JHL6540 Thunderbolt 3 Controller per each side and you won't see any differences as well. The only issue you can have is the what the device you have plugged in may require power and needs to be feed from the other side of the power connection as the Controller chips duty cycle drops when it's being powered and also delivering port to its mate port. Basically you need to segregate as best as you between the left and right ports on how you power your system and the external devices you have also plugged in.
  • Ok so my company deals a lot with Mac's, our user base is about 80-90% Mac users, 99% of the time things go well but every now and again something odd comes up. 1st one: New Mac, 8GB Touchbar. When charging and using Zoom, it sometimes slows down to a crawl, freezes and stutters. I re-imaged it, i found no issues, couldn't replicate, sent back to user. Happened again. Advised on SMC and PRAM reset. Changed charger to a 30W from a 61 (which came in the box) and an 87W, see how they do (not arrived yet) Also saw this with someone else who has the 16GB model like me, high spec version, which has 4 USB-C ports. I charge on the right, when i'm working on a Mac i charge from the right. They must be charging from the left because i don't get them faults. Now i know why two of the users have this issue, however the 8GB version DOES NOT HAVE USB-C ON THE BLOODY RIGHT HAND SIDE!!!!! Come on apple? This is insane.