How non-linear is battery life?

[scubadoo]

If a battery spec says:
"8000 cycles at 80% DOD at 0.5C"
Is there any way to guess how many cycles it'll do at 50% DOD or 0.25C, or elevated temperatures, or any combination thereof?
...

I will let you know when we get there.
Our 4 cell 300Ah Sinopoly battery has now survived 10 years of fulltime travel being typically depleted about 35% each evening. It also starts the truck engine often multiple times a day.

Number of "cycles"? I will leave that to some theorist.
Talking capacity in Ah it has dropped from the original 315 to just 299 at the last annual November capacity test. Not sweating yet.

I suspect that the battery will eventuality die from some other cause rather than any "cycle" count losses.