10 Replies Latest reply: Jan 12, 2015 5:37 AM by Holzfreiweiss
lukewd Level 1 (0 points)

hello all. i am considering upgrading from a Macbook Air to the new MacBook Pro with Retina Display.


However, i would first like to know what happens if you plug the new MacBook Pro with Retina Display into the older Air's 45w MagSafe 1 adaptor?


The reason for my question is that I have bought several spare 45w magsafe adaptors and have them in places like my home study, and office desk. this saves me having to pack one up whenever i move location. i am 100% aware that the older ones would need a converter to make them fit.


but the real question is, will the older 45w magsafe adaptor harm the new MacBook Pro with Retina Display? if not, will it power it at all?


i dont mind if it doesn't actually charge the laptop but rather just powers it. could someone please test this and let me know. thanks.

  • captfred Level 7 (26,290 points)

    It's not recommended since it won't provide the required power.


    A quote from the linked article:


    Power adapters for Intel-based Apple notebooks are available in 45W, 60W, and 85W varieties. Although you should always use the proper wattage adapter for your Apple notebook, you can use an adapter of a higher wattage without issue.



  • wjosten Level 10 (94,210 points)

    It will get extremely hot & any long term use will most likely burn up a 45W power supply if used with a Retina.

  • SOJHA Level 1 (5 points)

    It's like trying to use vodka to power your car. The 45W supply simply does not possess the required current to charge and power your 15 inch powerhouse.

  • lukewd Level 1 (0 points)

    hi guys, thanks for the input but this did not really answer my question.


    i had already read that apple document, and personally i found it a bit vague.


    can anyone tell me with real world experience what happens when you connect a MBP Retina into a 45w Magsafe 1 adaptor? will it even power the laptop at the very least, if not charge it?


    the reason i ask is that i now have 2 spare 45w magsafe adaptors, and i want to know if they are going to be completely useless if i upgrade to a MBP Retina? or will they at least keep the Retina powered whilst it sits on my desk?


    thanks, and please try to be specific.

  • Nelsonn Level 1 (0 points)

    45W can't use to be charge 85W, it will cause your 45W charger gone, even it can charge, after few weeks charger will burn itself, and ur battery keep using with high Watt but just coveer with little 45W will damage your battery too, prefer not to do that, unless emergency.

  • wjosten Level 10 (94,210 points)

    You will not damage your computer using the 45W adaptor. Depending on what you're doing, it simply won't be able to provide enough power to both charge the battery & power the computer. While your computer is off or sleeping, it will charge but slowly. The most that can happen is the adapter fails from heat, after all it is being used for something it was not designed for. Despite my suggestion not to do this, my daughter in law does this regularly & has been doing so for the past 6 months...she got an Air for Christmas & also owns a 15" Pro. If there were any chance of damaging your computer, Apple would design these things so that they could not be interchanged.

  • lukewd Level 1 (0 points)

    Thanks, this is the exact answer I was looking for, and it is what I expected to be the case. I just wanted a little reassurance...

  • wjosten Level 10 (94,210 points)

    You're welcome.


    My daughter in law keeps the 45W adaptor at home & the 85W adaptor at work...doesn't want to spend the money for a second 85W adaptor...despite my suggestion she do so. Works for her .

  • Douglas Hardman Level 1 (5 points)

    I like the 45W because it weighs a LOT less than the 85W. When I'm traveling, the 15" already weighs 1lb more than my MBA, so adding a power brick that also weighed more wasn't something I was excited about. I use the 45w in my briefcase, and only use it if I'm running out of juice while I'm giving a presentation or something. With the battery life of this thing, I can run almost all day without an issue.

  • Holzfreiweiss Level 1 (0 points)

    What would happen if the PRO needs more energy than 45W (e.g. gaming)?

    it must detect, there is not enough power supply, and should switch to battery.



    For me it works perfectly!  (meanwhile i don't run mine CPU on 100% usually, the adapter is not even really hot)