I couldn't say the precise reason why charging to a higher voltage reduces capacity faster. It is a more chemically extreme state for the battery
There are lots of tables online showing how many charging cycles you get out of a battery vs how fully you charge it
Other things to keep in mind for lithium ion battery life.
Avoid the following no matter what:
- leaving the batteries charged to 100% constantly without using them
- leaving the batteries depleted to 0% constantly (even worse than the above)
When the lithium ions are left overwhelmingly...