Hi cdcorpe,
Every time a battery is cycled there is permanent irreversible damage.
The higher the voltage the greater the "shaling" of the positive plates. However, one needs to look at batteries in the same manner as gasoline. They are a consumable item, that sooner or later will need replacement.
The difficulty is that it is damaging to over charge, under charge, delay charging to 100%, and failing to equalize. There is even a term for proper charging protocol. It is called "dancing on the needles".
It appears that part time folks with good solar systems get more years of use from their battery banks. Folks with smallish battery banks need more solar than folks with medium banks, again because the ideal is getting to 100% state of charge.
Full timers have to have a much larger solar system to get that same result as they need to get to 100% state of charge at least once a week (every day if they can).