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2.3GHz, 2.6GHz, or 2.7GHz quad-core Intel Core i7 processor (Turbo Boost up to 3.7GHz) with 6MB shared L3 cache.

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MacBook Pro won't turn on after battery replacement

I replaced the battery in a mid 2012 macbook pro.

When I plug the magsafe in there is no color on it, but the two fans start to run. The speed on the fan go up and down.

Can anyone help me with this?

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Why did you replace the battery? Was the system working before?


Well. The mac didn´t work without a charger..

I think it might be the SMC but I hope not :P


So we have no back story here just a dead mac? And you decided to just replace the battery? You really need to do some basic diagnostics before you take action. Otherwise you're just playing 'Wack a Mole'


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If you haven't replaced the battery yet lets NOT DO THAT!!

Instead lets walk through a basic diagnostic process to find out whats wrong:

  • You need to ask the customer for some level of background info like what happened when it stopped working, Did the system get banged or dropped? Did the system encounter a liquid spill and when. Did it get wet from rain or sitting down on a wet surface?
  • Next inspect the system for physical damage what do you see?
  • In laptops inspect the MagSafe connections and the MagSafe charger do they look good? Refer to this Apple T/N: Apple Portables: Troubleshooting MagSafe adapters making sure the adapter is the correct one and the cord and the connector ends are in good shape.
  • Test their adapter with the system what happens. Test the system with your known good adapter what happens
  • If the system has an onboard battery tester try it out what does it show
  • Listen... Do you here the fans
  • Do an SMC reset and check again any sound?

Now lets get the answers and post them here under each bullet point.

Update (02/01/2018)

OK, so the MagSafe connector was dirty which is why it was having troubles.

When you replace a battery you need to let the system charge the battery fully, then you need to drain it fully and do a SMC reset. We do this again a second time! This calibrates SMC to learn the low point of the battery. Without going through this calibrating process you can encounter odd behavior of the system shutting down (sleep mode and/or deep sleep mode depending on what you have set in energy saver).

How to reset the System Management Controller (SMC) on your Mac & Use the Energy Saver settings on your Mac

Here's some other sites run down on battery calibration:

I would also down load this free app: CoconutBattery This is the goto to see whats happening with your battery, MagSafe & the systems charging logic.

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First I must say I really appreciate your help and advice @danj

Thank you so much.

A little update first: I got the mac to start up, and it works fine with the charger. And now the magsafe has right colors. It don´t work without the charger tho. Even with new battery.

To your bullet points:

1: Battery status was: Replace Now. The battery last for about half an hour. Worked fine with charger. No damage or liquid to the mac.

2: No physical damage. No sign inside mac either.

3: I disconnected the magsafe connection and cleaned it (might have been the reason it started now)

4: Works now, so thats not an issue.


6: Works now, but the fan did start when the charger was connected.

7: Works now.

So the question now is, why don´t it work without charger.. Battery shows 45% but are not going up..

You might have other tips? :P


Ok. But the problem is that the mac shut down when I unplug the charger. When the charger is connected the battery status is standby on 45%. Shows that it charging tho.

Will check the app tomorrow.



If it's shutting down you have a charging logic issue.


Thank you for all the help @danj :)


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alex will be eternally grateful.
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