There would have to be some kind of argument that the bigger battery leaves capacity on the table during its life somehow, which would mean the battery is still expected to be useful when the car is retired?
It is much lower energy density than typical BEV batteries. It is also rated at 20x the cycles and can be charged and discharged very quickly with minimal issues.
The technology has come a long way from the NiMH cells that die after a decade.
I would think that it would be primarily a function of how much of the battery is treated as a 'reserve'. If you have 10-20% set aside that is not "useable", regardless of total capacity, then you could get similar cycles.
There's also the possibility for using super-caps taking some of the brunt for high discharge (2-4s) events which could help with longevity. How expensive are they for these type of use case?
If each cell in a 15kw battery discharges at 1c to move a car, each cell in a 45kw battery discharges at .33c.
Same goes for charging.
Might be diminishing returns, but discharge rates over 1c harm longevity.