Should an iPhone recharge when plugged in to a MacBook Air which itself is plugged into its wall charger?

My MacBook Air was closed and plugged into its wall charger. The green light on the power cord was lit. I plugged my iPhone 4S into the MacBook Air USB port under the MagSafe connection. I went to sleep. When I awoke seven hours later, the iPhone was at 30% charge. I thought it would be at 100%.

Is something wrong?


I am not sure about MacBook Air, but in my MacBook Pro (Mid 2010) it will charge my iPhone if the MB is active (powered up and not sleeping) and it will also charge my iPhone when sleeping, but only if the iPhone was plugged in before the MB went to sleep.

If your MB is shut down (not active & not sleeping) it will not charge your iPhone.


One of OS X/MacBook updates must have changed something at some point. Now, when a MacBook is plugged and sleeping and you plug in an iPhone, the MacBook will silently wake up, start charging the iPhone and fall back to sleep. It all happens with closed lid.

  • 3
    Whoever downvoted my answer, please provide feedback why. I'd like to know what's wrong with it. – Michal M Nov 10 '11 at 15:42
  • As you suggest, I will try plugging the iPhone in while the MacBook Air is awake, then closing the MacBook Air for the night. – Thomas L Holaday Nov 11 '11 at 3:58
  • that worked. A MacBook Air is willing to act as a powered USB hub, but I have to ask it first. – Thomas L Holaday Nov 11 '11 at 14:23
  • Yes, I can agree with this. I had the same problem with our MBP (late 2011). I figured out this exact same thing. – daviesgeek Jul 21 '12 at 1:02

If you plug in when the computer is asleep or shut down (even if it is connected to mains) iPhone will discharge slowly

Charging iPhone requires 1000ma which is more than the standard 500ma draw from a USB port. To allow a high current device to take more than that it must negotiate with the host machine, which will not occur if the machine is not active.

You used to be able to look in your console logs while connecting iPhone to see the negotiation happen. Not sure if this is still the case

  • Are you referring to the Battery Charging Specification mentioned here? – Chris Frederick Nov 10 '11 at 20:55
  • That is a way for devices to negotiate which will work for 'passive' devices such as chargers however as mentioned I have seen an active negotiation process initiated between an iPhone and MacBook – Kevin Nov 10 '11 at 21:32
  • @Kevin are you sure charging iPhone requires 1000mA? Most PCs do only 500mA and at least with mine it is fine to charge both iPhone 3G and the new 4S. – Michal M Nov 11 '11 at 8:41
  • For recommended charging iPhone requires 1000mA. It will charge slowly (if not in use) on 500mA. You may find your PC port is providing more than 500mA if it is recent as many support higher power devices. Incidentally iPad requires 2000mA and will not charge at all on a 500mA port (and will tell you this when connected) – Kevin Nov 11 '11 at 14:27

It will only charge when the laptop is active, eg. not sleeping. Prevent sleeping your computer (you will need to leave the lid open and possible adjust your power management settings), or use the adapter for the iPhone to plug it into a wall socket directly. I'd go for option 2, save the electricity.

I recently also stumbled upon the following accessory, it's pretty neat and probably would serve you well: http://twelvesouth.com/products/plugbug/

  • Interesting - had never seen the plugbug. Very cool if you have only one plug! – JW8 Nov 10 '11 at 17:15
  • +1 for PlugBug. Although doesn't really answer the question asked, it's a very clever solution. – Michal M Nov 11 '11 at 8:41
  • I'm not sure how it didn't answer your question? The iPhone will not charge when the laptop is asleep. Could you specify? – Gerry Nov 11 '11 at 12:44
  • @Gerry, the first part of your answer was apropos of my question, but perhaps +Michal M has a different question in mind. Thanks for the pointer to the PlugBug. – Thomas L Holaday Nov 11 '11 at 14:22
  • @Gerry It's not a valid answer, because MacBook can and will charge an iPhone when sleeping as I explained in my answer and what Thomas confirmed. – Michal M Nov 11 '11 at 15:07

Looks like with the introduction of the authentication chip in the Lightning cable Apple is requiring the Macbook Air (MBA) to be up and running to charge your iPhone.

I found that by using a USB-Lightning adapter on an old 30-pin USB cable the laptop charges my iPhone 5 from standby. Tested it a number of times.

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