If you wanted to maximize the lifetime energy thoughput of your Li-ion cells,
would you charge to 80% every time, or 100%?
The cells last longer (I assume this means before they lose capacity), at 80%.
But you get more in and out, with each charge at 100%.
To come out ahead, they would need to last 25% longer at 80% charge.
Which is it? 80% or 100%?
Show your work 
wle
In general charging to 80% and recharging at about 30% will give the most cycles.
But there is much more to this, keeping the temperature cool, not punishing the cells on high charge or discharge rate, storing the cells around 50% when not used for long periods and so forth.
All that said cells are not expensive so some may see no point in babying them, but conversely if you do see the point then you can put in the work and have your cells live a long time.
As for citations for all this, i don’t have any off the top of my head, but you can run what i have said through the google and read through the results.
There was also another thread recently on BLF about this, if anyone remembers the title of it a link would save a lot of repeat keystrokes.
True - cells are cheap - but I’m also concerned with Phone Batteries, which are not.
(Though you can not conveniently cut charge off at 80%, that I know of.)
wle
I charge my cells on the lowest setting and don’t leave them in hot/cold environments. Otherwise, they don’t get babied. I feel like they’re going to degrade over time either way so no point in worrying.
If you have Android then get Accubattery. It beeps at 80%.
I made a lot of posts in this thread explaining how batteries work