I have the latest Retina MacBook Pro MacBookPro11,2

I quite often have the CPU at about 400%-500% usage (e.g. 4-5 cores at 100%) and also do GPU intensive tasks. While this is happening, the battery can actually discharge even though it is plugged in. This has happened since I first got the MacBook and is not something which has developed over time.

I have the model without a dedicated GPU (Intel Iris Pro only), and I have an 85 watt power supply which came with the MacBook

This is very irritating for me, is this a fault or normal behaviour?

  • I noticed the same thing ( MBP Mid 2014 i7 ) and for a £2000 laptop, it's unacceptable to not be able to use it on 100% for more than a few hours. – AntouanK Apr 14 '15 at 13:20
  • @AntouanK, I got a new power supply for unrelated reasons, and I've not been able to reproduce the problem since. My old power supply would get extremely hot on the cable, and eventually melted itself, turns out there was extra resistance in the wires for whatever reason. My new 85 watt supply is keeping up with the MacBook load perfectly – Joseph Apr 15 '15 at 15:26
  • Easy way: get "bitcoin-qt" and let it run for a few hours. You'll see the charge going down, even though it's plugged in. I have the stock charger that came with MBP. I'll see if I can try with another one. Thanks. – AntouanK Apr 15 '15 at 16:22
  • Yeah, mine used to do just that under heavy GPU and CPU load. After getting a new (official) power supply, it's not happened again even in the same situations as the last one – Joseph Apr 16 '15 at 21:46
  • Same things are happening to my 2011 MBP, and it looks like designed behaviour. If you are curious, you can find your processor's TDP (45W for me) and compare it with charger power. – Dan Jan 22 '17 at 11:51
up vote 0 down vote accepted

It is a known problem: https://discussions.apple.com/thread/3069428 Someone has calculated the max wattage draw of a MBPr, but I can't find that a.t.m.

Try to reset the System Management Controller (SMC) on your Mac, following the instructions mentioned in this Apple Support article: How to reset the System Management Controller (SMC) on your Mac.

I see this as a design choice - works as designed and functioning as built situation. All engineering and hardware design is an exercise in tradeoffs and many of the goals compete against each other:

  1. reliability of the parts as they age
  2. ability of manufacturing to make the device reliably and repeatably
  3. cost of parts
  4. cost of manufacture
  5. speed to diagnose and repair
  6. durability of repair (nothing makes us mad like looping repairs when the issue isn't fixed or more issues are caused by a repair for something else)

I haven't even got into the more relevant design decisions like which CPU chip to put it and whether the higher CPU model gets the same power supply and battery as the lowest performing CPU model. Or whether the CPU you chose can out run the power supply since the battery can and has always for the last 10 years been able to supply far more current on demand than the charge rate of the battery from the AC power supply transformer. The only intel based Mac product that can't outspend their power supply are ones that plug into mains. No portable Mac can keep up with a fully running CPU/GPU when cooling is good enough to keep thermal throttling from kicking in.

I'm not at all saying you are wrong to be irritated, just that this was a conscious decision made by teams of people knowing some times their design won't keep up and then management trusting / approving those design decisions and shipping years of product with that decision. When viewed from the lens of CPU shouldn't outpace the power supply, this is a compromise. When viewed from other lenses (lightness, parts management, reliability, supply chain management), this is an excellent/beneficial decision (or still compromise). I hope this helps you know you're not wrong and that this would be something you consider when you choose how your processing load gets run. Whether you can offload some tasks to the cloud or if you need to be tied to mains power since you can't accept this sort of tradeoff for your needs.

  • The problem never came back after I got a new power supply; I can only assume my previous one was faulty. – Joseph Aug 31 at 22:14
  • Cool, I assumed you ruled that out so my fault. Glad it was just the adapter. I’m sure you could overdrive a great adapter, but happy your usage wasn’t too far in the red. Please put up an answer and select it if you don’t want more answers, @Joseph – bmike Aug 31 at 23:00

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