I just got a new 15" macbook pro to replace my old macbook. I have a couple extra chargers for the macbook, and I'm wondering if it's safe to use them to power the pro.

Normally I wouldn't think it's safe, since the macbook's charger is 60W while the pro's is 85W. I'd worry it might damage the battery or not be able to fully power the laptop.

However, my dad has apparently been using an old macbook charger to charge the pro he got a few months ago, and claims it's been working fine.

I'd love to be able to use my old chargers so I can leave one at work instead of lugging around a charger in my bag every day. But I'm worried it might damage the battery's health, and since they're no longer replaceable I'd really like to avoid that.


It is quite safe. I have used my laptop (HP) with underrated power supply for almost two months (waiting for replacement part) and there are only two issues with it:

  1. Your battery will take longer to charge.
  2. From time to time, when you do something that needs more power (e.g. watching video), it will completely stop charging battery. Once your power requirements go down, charging will resume.

If you keep battery always topped, I see no problem with that arrangement.

  • I did that with an old Dell machine before, but the lower wattage adapter wouldn't charge the battery and caused the CPU to run at a lower speed. I wasn't sure if the mac would have different logic for using the other chargers. – Herms Jan 3 '10 at 20:47
  • It probably depends on what exactly are power requirements. In my case original was 90W and I used 65W one as a temporary replacement. – Josip Medved Jan 3 '10 at 21:35

You won't notice the difference when you are just using your macbook pro, but when you stress it (100% cpu and gpu) you could damage the 60w adaptor. You won't damage the battery tough.

  • good to know that stressing it could damage the adapter. sounds like if I have one at work, where my laptop isn't generally stressed (mostly just plays music) should be ok. – Herms Jan 3 '10 at 20:47

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