You have to find the balance between number of cycles and the depth of discharge. It's not good to discharge and it's not good to charge to 4.35V.
There is no %, the percent is just an approximate. A more precise figure is voltage, a Li-ion batteris full at 4.35V and dead at 3.5V. 80% is really 4.0V. So aiming for 4.0 to 4.1V is really the ideal.
Charging a cell to 4.2v will give it a life of about 300 cycles.
Charging a cell to 4.1v will give it a life of about 1000 cycles.
his chart is simply a guide to use voltages to determine how full a Li-Ion cell is.
4.2V = 100%
4.1V = about 90%
4.0V = about 80%
3.9V = about 60%
3.8V = about 40%
3.7V = about 20%
3.6V = empty
< 3.5V = overdischarged