I've had this issue many times over the years on and off with a late 2011 mbp and a late 2009 mbp. After trying all of the suggestions on the thousands of threads out there about this (google: "osx kernal_task") there was one comment I finally found after all these years (<a href="https://discussions.apple.com/message/27901055#message27901055" rel="nofollow">https://discussions.apple.com/message/27901055#message279010...</a>) that has so far been my fix for the past year or so on both. I used to always keep them plugged in to an outlet but now I only use them un-plugged until ~30% then charge back to 100% and un-plug again. I haven't seen the issue since so I figured I'd put this here since it's not a common solution posted to the "osx kernal_task" term.<p>Relevant bit from the comment "Eventually I realized that the issue seemed to be related to heat. The kernel task spins up CPU cycles to stop heat generating processes from maxing out the CPU and overheating the macbook. About the same time I also realized that the problems seemed to start happening about the time my battery reached 1000 cycles. I have still not replaced the battery so I am not sure it will fix the issue completely. I do know that when the power is not plugged in the kernel_task seems to stay relatively low on the CPU usage list. My battery only lasts about 30 minutes now on low usage so I keep it plugged in all the time. When the kernel_task process pegs my CPU I unplug the power and the process drops back down to normal."