I believe the watages aren't the only difference. If you look at both carefully they should be marked with output voltage. I believe the air is 14.4, and the pro is around 18 v. If they are different I would not suggest it. even if others have done it. It's not worth the risk.the damage may be immedieate, or longer term, or even not at all.
This is incorrect. From this Apple technical support note:
"Power adapters for Intel-based Apple portables are available in 45W, 60W, and 85W varieties. Although you should always use the proper wattage adapter for your Apple portable, you can use an adapter of a higher wattage without issue.
For instance If you have a MacBook (13-inch Late 2009) that normally uses a 60W adapter, you can also use an 85W adapter with that computer. You would not use a 45W adapter with that computer; it would not provide enough power for that MacBook. Using an adapter of higher wattage than the adapter that came with the computer will not cause the computer to charge more quickly or otherwise operate any differently than using the adapter that came with the computer. "
I'm sure apple knows what they are talking about. It's possible the computers have a secondary device to limit the voltage inside the actual computer. It would appear odd to me they would offer the power supplies in different voltages then. I have had in the past , with other manifacturers, technical support that was not correct, or had lost something between the technical and writing departments. I've had repair manuals that have contained the same damaging technique in them for 20 years, even after authorities in the subject have notified the publisher. a 20% increase in voltage is significant to me, and I would not be comfortable with it.
All MacBooks with the MagSafe connector use the same voltage!
As a number of folk have confirmed, you can use a more powerfull adaptor, but not the other way round.
It's a simple case of Ohm's Law, the power is related to amount of current drawn by the unit. That's why you can plug a table lamp into the same socket as your kettle without problems, as they both use the same voltage but draw different amounts of current.
In addition to Apple official answer above,
here is my 2 months experiment:
I have using Macbook Pro power charger to charge mac book air 13 inch.
so far, I have not seen any problem like heating up a body, a charger or code.
i hav seen that link in the earlier post. was there an offical apple repair tech responding among the posters that I missed? I usually don't have much faith in tech support that are reading a script, that have no practical hands on experience.
I do believe the outputs are specified in the owners manuals are different:
: 18.5 V DC, 4.6 A http://manuals.info.apple.com/en_US/MacBook_Pro_17inch_Mid2010.pdf
There may be some trick circuirtery to accomidate this, I don't know. OHMs law is useful to deternine power current and resistance. I don't think think it easily reflects semiconducter voltage stability.
I do believe that using too much voltage is a bad thing. How much is damaging to an apple, I do not know. I can tell you what happens if you put a 6v light bulb on a 12v car battery. I know if you put an average car radio designed for 12-14v range on an 18v converter, it will get very loud before smoke comes out. I do also believe that if i put a 24v tractor battery in my car, the ecu will not be long for this world.
Reading through comments on a variety of foriums, I see many saying it is safe, but none saying they encountered a problem. The concensus seems to be that it is safe. I expect that means the computers have another voltage limiter in them. I think someone with firsthand technical experience would have commented somewhere if there was a conflict, but I could not find it.
At the risk of repeating myself and all the other posters. YOU CAN USE ANY LARGER PSU ON A SMALLER MACBOOK.
There is an easy way to prove this. The 24 and 27" Apple Display has a MagSafe cable to allow you to plug ANY MacBook into it, which if Apple didn't approve of, they wouldn't sell it.
Otherwise, Apple would have to make 4 different versions of the 27" screen, which they don't
The voltage on the PSU is irrelevant because this is a no load condition.
You can rest easy and have an 85Watt PSU and plug any size of MacBook into it.
As far as a second battery supply goes, HyperMac sell external battery units for Mac kit
Mike (Apple dealer since 1989)
I see that on http://support.apple.com/kb/HT2346
Note: Adapters that shipped with the MacBook Air (Original), MacBook Air (Late 2008), and MacBook Air (Mid 2009) are not recommended for use with MacBook Air (Late 2010) models. When possible, use your computer's original adapter or a newer adapter
This one really surprised me that Apple says there are differences between MacBook Air model chargers!?!
This seems really strange, especially when you consider how small (and gray) they make the print on these.