Can you use the 65w MacBook Power Adapter with an 85w MacBook Pro?
(Disclaimer – This was my experience, if you try this and blow up your laptop or house, it’s your fault).
I only post this because I could not find any definitive answer when Googleing last night, so I figured I would share my experience. When I got home last night, I realized I forgot my new MacBook Pro’s (Nov 2008 / unibody) power supply at Macenstein‘s labs, but I really needed to work on some award-winning articles. Once my MBP’s battery hit 37%, I began to panic (btw, there’s no way the new MacBook Pro gets close to 5 hours of battery life, even with the performance turned down). I looked around and noticed I had an extra power supply for my (October 2007) white MacBook lying around, so I figured, “What the hell, they both have MagSafe connectors! Let’s give it a try”. Sure enough, despite being rated at 65w, and the MacBook Pro claiming it needed 85w, the MacBook Pro charged fine. I occasionally felt the MacBook’s power supply to see if it was going to over heat or anything, but it remained as cool/warm as it ever did when charging the original white MacBook.
I had found posts about going the opposite way (using an 85w to charge a 65w MacBook) and those posts seem to indicate it works â€“Â there is some auto-sensing thing-a-ma-jig in the MagSafe connector that allegedly scales back the juice (NOTE – I have not tried this).
For the record, I first changed the energy settings to “Better Battery Life” from “Higher Performance”, logged the MacBook Pro out, and I turned the screen brightness down quite a bit. However, it charged fairly quickly, so I’m not even sure that was necessary. I went to bed with the MacBook Pro charged to about 88%, and left it plugged in overnight, and woke with a 100% charge and no house fires to report. According to iStat, my MacBook Pro’s batery still has 100% health, so as far as I can tell, this did no damage to the MacBook Pro.
So in conclusion, yes, it works â€“ although I am still keeping an extra MacBook Pro power supply on my Christmas list to leave at the lab.