Lithium ion batteries are interesting, but I think they lack the potential of ultracapacitors.
From http://www.rexresearch.com/weir/weir.htm and
http://thefraserdomain.typepad.com/energy/2006/01/eestor_ultracap.html
... new ultracapacitor made by start-up company EEStor of Austin TX.
-- It is a parallel plate capacitor with barium titanate as the dielectric.
-- It claims that it can make a battery at half the cost per kilowatt-hour and one-tenth the weight of lead-acid batteries.
-- As of last year selling price would start at $3,200 and fall to $2,100 in high-volume production
-- The product weighs 400 pounds and delivers 52 kilowatt-hours.
-- The batteries fully charge in minutes as opposed to hours.
-- The EEStor technology has been tested up to a million cycles with no material degradation compared to lead acid batteries that optimistically have 500 to 700 recharge cycles
It may recharge in minutes at a service station that's connected to a major power line, but not at home
To recharge a 52 KWhr battery in 10 minutes would require an electrical source able to deliver over 300,000 watts