While these are good guidelines, I came to the conclusion that life's too short to spend so much mental energy on this. If your devices need to be charged - charge them. That's it, that's the only rule.
Lenovo has a tool that can keep the battery at around 70%. If you are 80% working in the same location, then it can really keep your batter life longer. If you are moving all the time, then certainly keep it charge to 100%.
Apple has started doing this and I can't say I am impressed. When I unplug I expect my laptop to be at 100% not randomly at ~80% based on a guess as to when I might unplug.