Great post and interesting subject. My understanding is that once rechargeable batteries do not recharge anymore, after so long a life, then they are only worth the recycle value of their materials less some kind of processing fee.

Here is a brief read on the subject of the cost and useful life of these batteries:

Major concern with electric vehicles is the state of current battery technology. Lead-acid batteries have several downsides to them such as their heavy weight, being up to 1,000 pounds per pack. They have a limited capacity and are slow to charge, they have a short life of three to four years, and they are expensive (currently $2,000 for the typical battery pack). NiMH batteries are another type available for use in electric vehicles. The range of the car will double and the batteries will last ten years, however, cost of the batteries today is 10 to 15 times greater than lead-acid. It is likely that over the next several years NiMH and lithium-ion battery packs will become competitive with lead-acid battery prices. Electric cars will have significantly better range at that point. The problems with battery technology lead to much interest in using fuel cells. Compared to batteries, fuel cells will be smaller, much lighter and instantly rechargeable. When powered by pure hydrogen, fuel cells have none of the environmental problems associated with gasoline. It is very likely that the car of the future will be an electric car that gets its electricity from a fuel cell.

Rest of the story:

http://www.faculty.rsu.edu/~clayton/...