When I think of battery degradation I think of a behavior similar to the one illustrated in the following graph:
http://batteryblog.ca/wp-content/uploads/2013/07/BAK_1-1600-Cycles2.jpgThere is quick degradation in the beginning, followed by a nice and slow decent until it reaches a point where the decent accelerates exponentially reaches bottom and then straightens up again.
Two things that I wonder about:
1. Why does it reaches an exponential decay phase? Is it because the demands on the batteries remain the same even when the capacity of the battery is diminished? What was a 20% to 80% cycle when the battery was 100% becomes a 5%-95% cycle as the battery reaches 90%. BY the time the battery gets to 80% the original 20%to 80% demand becomes less than 0 and more than 100% quickly ruining the battery.
If that is the case, then maybe significantly lowering the demand of the battery to appropriate levels significantly extends the battery life in a different application.
2. When the battery reaches extremely low capacity the decay stops. The charge seems to be very small, but using massive parallelism of used up batteries they could be useful in applications where mass/volume doesn't matter, like grid storage. Of course that is subject to a possible "Calendar function" as described by Bob Wallace.