[Buck_W]

The 85W Mag Safe Power Adapter has gone bad. Apple is in the process of shipping a replacement. In the meantime, can I use the 65W adapter from my daughter's MacBook to charge my MacBook Pro, without screwing anything up?

[Simon]

Yes. It will charge, just slower. The other way around works too. There's nothing you can break.

Nitpick: it's actually 60W for the MB charger.

[imitchellg5]

It will charge very slowly (or not at all) when you are using your MacBook Pro, but nothing will go wrong.

[Eriamjh]

You may have to shut down/sleep the notebook to charge the battery. It will likely power it to use without charging if it is on.

[Spheric Harlot]

In fact, if you're taxing your MacBook Pro, the battery may still discharge even though it's connected to the power supply, but it will discharge a lot slower.

The power supply will get HOT. I've had one shut down on me temporarily, a couple of years ago.

In a pinch, you can do it. I'd sleep it to charge, but that's just me.

[Buck_W]

Thanks for the replies, the new one is being overnighted but I don't know whether it was shipped today or will be tomorrow. Simon: you're correct - it is a 60W

[Simon]

An idle MBP draws about 20W. That leaves 40W for charging. Under heavy load you will see that charging becomes extremely slow. But you won't see discharging unless you'd try this with the MBA's 45W adapter.