A buddy of mine is working with provincial electricity authorities to create a 'second use lifeline' for car batteries. Even if a battery pack only has 70% of its capacity left, it can be stacked in a steel box with a dozen others, and used to balance demand on the grid - absorbing excess capacity minute-to-minute, and putting it back on the grid when demand is highest. They would continue to use the pack until it was down to about 45-50% of its capacity, then send it off for recycling. The only reason it hasn't been rolled out anywhere is that the competition for used car batteries is fierce.