Tesla motors already has a plan to do that with their car batteries . I'm not sure of the time period but they do acknowledge that the batteries drop ultimate performance in a few years and then have a long life of around ( I think ) that 85% you mentioned.
I'm pretty sure that they already have a system in place to ' recycle ' there own batteries . The idea is to use them in houses to absorb energy and then give it back to the grid at peak times.
