Upgrading to Windows 10 (A story about CPU consumption)

This is a short story about excessive CPU usage on a machine upgraded to Windows 10. I had very recently upgraded my Lenovo ThinkPad X230 from Windows 8.1 to Windows 10. That upgrade was not seamless and I see from reviewing Internet articles that I am not alone. The upgrade story is described in the link below.
 
http://www.experts-exchange.com/articles/19299/Upgrading-new-er-Windows-8-1-machines-to-Windows-10.html
 
Now as a bit of background, I had learned with Windows XP Pro to start Task Manager at start up and set the option to "Hide when minimize". Hide it, and you see a green square in the system tray. Dark green means low or zero CPU, bright green for a long period (5 minutes) is an issue. (Try it yourself).
 
I have done this with XP Pro, Vista Business, Windows 7 Pro, Windows 8 / 8.1 Pro, and now Windows 10 Pro. Up to Windows 8 / 8.1, all the installs were clean (that is, fresh) installs. I eschew upgrades and always have. Through all these systems and for about 12 years, my machines have run CPU < %5 more than 95% of the time. This is minimum acceptable performance to my way of thinking.
 
Windows 10 is an upgrade and it seemed to force itself on me. I found no way to decline; however, I have said here in Experts Exchange before that I had intended to move to Windows 10, so this was perhaps the time after all.
 
So five days ago in the afternoon, my X230 became a Windows 10 machine and worked but not happily. Later that evening, I upgraded drivers, repaired or reinstalled software and generally put in 5 to 6 hours of remedial corrective work. By late Thursday night, I declared success, shut down and turned in. Next morning, I checked things out and submitted another article (link above) as the system seemed to be working fine.
 
During the day, however, and during normal use, I became aware that the fan was running overtime, but I had to pack and get ready to fly out early Saturday morning. The machine was otherwise working fine. I did notice only about 2.5 to 3 hours of battery time compared to the normal 4 hours or more.
 
Saturday, I started up, cleared my email, closed the lid (suspend and recover works perfectly on this Lenovo machine) and left for the airport. There was not much time to use the machine until back in my residence room (Corner Brook, Newfoundland University) about 10:00pm local time. I could then see (I should have seen before) that CPU was a constant 25% or more. I had to fix this before Sunday because the meeting would be in table groups in a sports complex and there just is not (and never has been at these triennial meetings) power at the tables. Charging tables are provided but you really want top notch battery life.
 
The first Google article I found suggested drivers and malware. No. I had already updated drivers and I don’t get malware on my machines. On to the next article.
 
The second Google article said stop Runtime Broker by turning off "Show me tips about Windows 10". Good idea and I turned off 2 or 3 notifications and restarted, but there was no real improvement. Later I discovered turning off System Settings Broker caused “Stopped Working” errors so I re-enabled the settings.  For information, the article that was current when I wrote this is listed below:

http://www.ibtimes.co.uk/windows-10-how-fix-system-ntoskrnl-exe-memory-leak-high-cpu-usage-1514316
 
The third Google article said turn off Windows Defender. Now this was strange because it was running, but it was not supposed to be running – Symantec Corporate turns it off. Turning off Windows Defender did not fix the problem.  The article that was current when I wrote this is listed below.

http://www.tenforums.com/tutorials/5918-windows-defender-turn-off-windows-10-a.html

Time to think!
 
If Symantec Endpoint turns off Windows Defender and (a) Windows Defender turns on after upgrade and (b) I did not have to reinstall Symantec after upgrade, then maybe I should Repair Symantec.
 
I shut down, started up, exited most running applications (One Note, NCP, SnagIt and so on), and run the installer setup file for Symantec Endpoint Protection. SEP says Modify, Repair, or Remove and I selected Repair. The repair took a while and then forced a restart.
 
I restarted and waited 10 minutes. Now CPU is <5% and stayed at < 5% all day Sunday. Battery life is good for 4 hours or more with 25 – 30% charge remaining. Charge at a charging station for 45 minutes over lunch and the computer was good for the balance of the meeting. Outstanding battery life (and CPU usage was back to normal).
 
Conclusion:
 
Upgrades to Windows 10 are now known to cause problems. On a good base machine, upgrade, then upgrade drivers and reinstall software as necessary. Take good look at Windows Defender and your own Anti-Virus application. You may need to re-install it.