After removing the battery from a MacBook late 2009 following a battery fault, the computer always runs kernel_task at 100% CPU utilization. I assume the process ends up in some kind of spin lock when looking for the battery and failing to do so. Is there a work around to prevent this issue? While waiting for a new battery, I would like to use the computer in a useful way on connected power.
The procedure mentioned here, involving the removal of one specific system file, will probably disable the sensor check and prevent the kernel task from gobbling up your CPU, while waiting for your battery: https://apple.stackexchange.com/a/146381/226332
MacBooks - all types and models - are capable of demanding - and getting - 20% to 45% more power from the battery than is available on the charge supply. The machine runs from the batteries exclusively at all times, unless the battery is removed or a problem is detected and it is switched out of circuit, whereupon the machine will self-throttle so as to not exceed the available charge current.
Usually when our Mac is running insanely slow with fans at full speed, it is a sensor issue. You may try to find on the Internet ASD (Apple Service Diagnostic) for your motherboard.
Alternatively you may boot with the D key pressed to enter the diagnostic mode.
Check which sensor (if any) is failing.
See Louis Rossman’s videos on YouTube. He talking about those issues.