Can a 60W MagSafe power adapter work interchangeably on a Macbook Pro that “requires” an 85W adapter?

Question

I have a 13" Macbook Pro that came with a 60W power adapter and a 15" Macbook Pro that came with a 85W power adapter. Can I use either adapter with either laptop? There seems to be disagreement in the Apple forums.

Answer 1

Apple's official word on the matter is:

Make sure the proper wattage adapter for your portable computer is used. Select the appropriate power adapter for your Apple portable computer. You can use a higher wattage power adapter, but you cannot use one with less wattage without potential operating issues. (here + discussion here).

So your 13" can use your 15" charger, but not vice versa.

I've never heard of it voiding a warranty (nor experienced it when we've used the wrong charger), but it's better to be safe than sorry.

Answer 2

You will not harm anything using the incorrect adapter. The charging circuitry in Intel Macs is very sophisticated and won't let anything truly bad happen.

Using the higher-wattage adapter with a low-power-requirement notebook will work transparently. The computer will only draw as much power from the adapter as it needs. Using the low-wattage adapter on a high-draw notebook will result in the adapter powering the computer OR charging the battery, but not both. If you plug a 60W adapter in to a MacBook Pro at 50% battery charge, the battery will just stay at 50% (or either drain or charge very slowly) while the computer is on. If the computer is asleep or shut down, the battery will charge at a normal rate.

Answer 3

Do NOT use a lower-than-spec'd power-supply with your portable. It will power on, but will be running in a brown-out condition, causing shortened life due to excessive heat.

We found this out the hard way with an after market power-supply on an iBook. It was just under the needed power output, causing the unit to always run hot, and eventually shutting down because of too much heat. After several months it got so it would run for 10-20 minutes then turned off, and eventually quit entirely. We tried getting it repaired, but it was too far gone.

Answer 4

This is a great question, and I kind of wish I'd thought to ask it before I started doing exactly what you're proposing. I suppose I assumed that the OS would warn me if using a lower/higher output adapter was somehow unsafe for my computer. In other words... keep in mind that what follows is only from my personal experience, and is far from scientific evidence one way or another.

Before picking up 2 15" mid-2010 MBPs in June, my wife and I were sharing a 2006 15" Core Duo MBP. The 2006 uses the 65W adapter, the 2010s use the 85W. We quickly noticed that the socket on the new ones was identical to the old. I figured that with Apple's attention to detail, it would be safe to try charging my 2010 with the old adapter.

Since it worked, we hooked up the 65W in the living room and put our 85Ws in our respective offices. Since June, both of our 2010s have been charged using both adapters interchangeably. I would say that mine (the 2.66GHz i7 model) has used it about 1/3 of the time. My wife's (the 2.4GHz i5 model) has probably used the 65W at or above 50% of the time.

Have I noticed any issues or degraded performance? Not one bit. In fact, I'm a bit surprised at how healthy the battery is on mine considering how often I use it without plugging it in. You can see my almost-current battery specs here. I thought that with as many cycles as I've put it through, my battery would be getting pretty close to 80% already. Also, I haven't noticed any difference in temperature when using a specific adapter.*

Bottom line... the only difference I've noticed is that the computers take longer to charge when using the 65W instead of the 85W, but even that difference has been minor.

*_{However, now that I'm thinking about it, I'll probably look a little closer at this.}

on edit:

After posting this, I took a look at my '65W' adapter. Apparently, it's not a 65W adapter after all, but an 85W with the older connector (the fat head connector). I always assumed it was 65W because of the age of our 2006 MBP... I guess the guy we bought it from used had replaced the adapter. So basically my answer is completely invalid (other than the stuff about there being no difference between the adapters) and should be disregarded :)

I'll leave this up for a day or two so that hopefully I don't lead anyone astray... On a side note, it's interesting that I've noticed the computer taking longer to charge on the older adapter. Oh, the power of the placebo effect...

Answer 5

I have been using the 60w adapter from my old 13"macbook pro(which was stolen a while ago) for my new 15" macbook pro for about a month because I assumed that all the cables or adapters are the same from Apple(since it is the case for the usb cable) and I did not realize until one day it turned off itself. Most of the time, my macbook pro was connected to the power. Now I have switched to the 85w adapter and everything works fine, thank god. my question is: will this cause any issue or damage to my battery or hard drive or other parts of my macbook pro?

Answer 6

I did use a 13'/65W power adapter on my 15'er for a long time.

What happened with me was that the battery got significantly bloated (visible from the outer aluminim shell and only after ~150 loadcycles) while still delivering proper batterylife...

Please take into consideration that this might be completely unrelated, probably. Plus my battery was replaced at no cost in an Apple store (Macbookpro late 2008, 1st gen unibody) while I'm still not sure if Applecare also covers the battery on 3yrs.

Answer 7

I'm using a 60W power adapter for my 2009 15 MacBook Pro. It runs fine if I'm doing light tasks, however, if I'm running an intensive application like Starcraft 2 on Bootcamp the battery will stop charging and drain very slowly.