After much research, I believe the cause is based around the following:
- iOS update process when updating the version - there is a conflict with an application which is running behind the scenes. The solution I would advise would be to see which application is running (by looking at the battery chart) and re-install.
- iOS update process when updating the version - make sure you de-activate, for every App before you upgrade: Siri, Notifications, Mobile Data and Background App Refresh.
- iOS update processionals when updating the version - once you have done all the above, then make sure Siri is off, I would clear in Safari 'Clear History and Website Data' (it is the only cache you can remove, the above steps will remove the cache per App, however, I do not know how to remove cache-memory).
This way you install, a new clean version of each App (I know a headache and along process if you have many apps). Hint:remember to take a screen shot per page of your App to help you remember which one you need to re-install)
For those who have already updated to the new version, then I would add one pre-step before re-implementing the apps by letting you phone discharge and then re-charge over-night.
If you have installed a 3rd party ant-virus software, then make sure you re-install this software first. Unfortunately, in my case there is a disparity between version stability between iOS and my Anti-vIrus: I have found by un-installing the Anti-virus software and then re-installing it, to be a stapler solution.
I just updated to 16.1.1 following the above steps, fingers-crossed I have stopped the heat and aggressive battery drainage.
Good luck