An update, I have been quite busy otherwise and pretty much preoccupied with trouble shooting the battery so I never took the time to test for any extended amount of time with El Capitan loaded and the battery unplugged. I tried that and it appears to be stable for a time up to even a few hours, especially if you don't run any apps but after a while the same continuous kernel_task 85-95% cpu useage crops up, sometimes even immediately from a restart after it has been exhibiting the problem, it really seems it can't be the battery.
So as I have noted with the battery unplugged and running off of the charger once the kernel_task 85-95% cpu useage starts even rebooting doesn't always help but it looks like if you shut down, unplug the charger wait a short while reconnect the charger and then start up again it runs fine for an hour or so and then the high kernel_task starts up again.
This has put me off Macs for life, I sit down in front of my rock solid Windows PC and appreciate it, bill gates and all!!