Hi jantimot
Just as a matter of interest which you may or may not heard of
There is a company which is trying to develop a software system to monitor each separate cell in a battery bank and charge each separately, which will allow a single cell to be isolated and replaced if the bank fails.
As you know in manufacturing there is no such thing as perfection so the approx 8000 cells are all different but are treated (now) as a whole with the life and capacity of the battery only as good as the weakest link,
IF they get this system working it will make a big difference to the lifespan but the complexity of the system with each of the 8000 cells on separate wiring, the cost maybe be greater than the cost of a new battery bank
