OK, back to the OP. As I reported earlier my SP3 has been having battery issues and running hotter than before since upgrading. It seems to be a bit random, but is happening more often than not. I little Googling reveals that it not an uncommon problem, and is also happening on other models but more often on SP3s.
In a year old article,
One user reports that it is caused by the Windows Installer Module and the Windows Installer Module Worker, which start in the background at random times and cause the CPU to work at bigger speeds. I can't fathom why it should start up again with the Win10 update though.
MS has not addressed this problem yet, but they are aware of it. And the pundents say that they will issue a fix soon.