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 Slow with Loud Fans after Battery Replacement

I just replaced the battery in my MacBook Pro using the iFixIt replacement kit. I got exactly the right battery kit: MacBook Pro, Retina Display, 15’’, Mid-2012.

Everything went smoothly when replacing the battery, but now my laptop is barely usable: everything is painfully laggy, including cursor movement/typing, and the fans run on maximum constantly.

I tried the SMC reset—no effect.

I downloaded coconutBattery to get some info, but not sure what to make of it:

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Any ideas what might be the problem? Thanks.


I am adding this screenshot of Activity Monitor, which shows that kernel_task is running at over 700% CPU capacity, whatever that means.

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Here are two screenshots of the app “TG Pro." Everything looks green except for the fans, which probably just adds to the mystery…

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I ran the Mac hardware test by holding “D” on restart, then following the prompts. Here is a photo I took of the results:

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Well, your battery info looks good! The kernel_task issue is caused by a sensor issue. Lets see if we can ID it using this app TG Pro post a snapshot of the main window so we can see all of the sensors (you may need to grow the window)

Update (01/12/2019)

The error you are seeing is: 4SNS TsOP - 124 - Palm Rest Temp sensor. You’ll need to inspect the trackpad connection on the logic board. Using a magnifier inspect the connects on the logic board and the cable you may have damaged one or two of them. If they are OK then the table its self or the trackpad are damaged.

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Thanks! Please see screenshots added in “Edit 2” above. Hope they are useful.


Sorry guy ;-{ I was hoping TG Pro would have shaken out the sensor. Often times when the logic board is taken out something is not reseated correctly. None of the monitored sensors have failed.

There are still a few sensors that are not monitored within TG Pro but are within diagnostics. Lets give that a try. Restart your system and press and hold the D Key. Let us know if an error popped up and its code hopefully we can decode it.

Reference: Mac startup key combinations


Nice—that seems to have picked up on an issue. See “Edit 3” above. I took photos of the other tabs of that dialog box, btw, but they didn’t seem to have any useful info so I left them out. Let me know if I should upload those as well. Thanks for your help!


Hmm, I did press pretty hard when I was scrubbing the adhesive off the backside of the trackpad. I think I’ll bow out at this point and let Apple do the necessary repairs. (I’m not jumping with joy at the thought of opening the laptop up again myself.) Thanks for helping ID the issue though!


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