Hans De Keulenaer's Library tagged smartgrids →  View Popular

After safety, the longevity of the batteries in a
plug-in hybrid is the greatest unknown. Can a plug-in
hybrid’s battery pack retain the bulk of its energy
capacity over 10 years of daily use and more than 4000
full-discharge cycles? (For a deeper look at the
challenges facing plug-in hybrid batteries, see “Lithium
Batteries Take to the Road”.)[ LINK:
http://www.spectrum.ieee.org/sep07/5490 ] As Don
Hillebrand of Argonne National Laboratory, in Illinois,
said tartly, “Batteries are the showstopper.”

Periodic demands from the grid, even for only a small
fraction of the battery’s stored energy, would clearly
affect the cells’ life span—but no one has data on how
much. Another open issue is the development of creative
financing models for replacement battery packs costing
several thousand U.S. dollars even after mass production
is achieved.

Third-party battery leasing could be one answer, if
combined with a secondary market for batteries whose
performance has fallen below automotive levels.
Carmakers, electric utilities, and large
consumer-financing groups are quietly batting around
these notions to see if they can build a financial model
that makes sense for all three parties.

It doesn't seem fair to the utility.  Utilities do more than just
generate and sell electricity to customers.  They also are responsible for
transmission (delivering the electricity) and reliability (making sure that the
lights work when you flip the switch.)