Thank you for replying and helping.
My PowerPoints are typically about 18 MB. They are mainly screenshots (hence the size). There are no animations, videos or audio.
I use the Office 2016 version of OneNote and this has local copies of my notes plus syncs to my personal live.com storage area.
I don't believe that I have enabled pressure sensitivity (do you mean the stylus?). In reality I mainly use it for pointing at the display as my handwriting is so bad!
I have display and sleep at 5 minutes when on battery (the default) although I believe that PowerPoint overrides this. I have now reduced brightness although I believe that I was previously using the default settings.
I was making notes on what started as blank OneNote pages.
I have Chrome on the computer but typically don't use it. I tend to use the default Edge unless there is a problem with it and a particular site.
Evernote, dropbox, gootmeeting, defender will run in the background. I have the full Adobe suite installed but am unlikely to use it (other than Acrobat) when on battery.
My device is the i7 with 8 gb ram and 256 gb storage.
I keep up to date with patches and have just installed the cumulative SP4 firmware patch installer.
Anything else that will be helpful?