A good little hybrid would need at least 8 kwhr of extremely good deep
cycle batteries.
Standard Sears diehard battery has enough zinc to withstand perhaps
150 super-deep 100% cycles, or 300 cycles at 75% and perhaps lasting
at best 600 cycles at 50% discharge.
A commercial UPS 170 pound 8D battery in this hybrid application is
good for 1 kwhr per fast one-hour discharge cycle, so you'd need
roughly 8 of those or 1360 pounds worth of battery. These batteries
are going to get pretty darn warm when discharged and recharged so
quickly, and you'll need something more like a VW bus or van in order
to accommodate 8 of these batteries that'll take up roughly a third of
the seating and perhaps 75% of the weight hauling capacity.
So every 3 years we install new batteries and we're good to go. Btw;
these 8Ds currently cost roughly $520 each.
http://www.google.com/products/catalog?q=8d+battery&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&tbm=shop&cid=1240007767239090202&sa=X&ei=zqtRT97nO-rhiAKAhuS0Bg&ved=0CIkBEPMCMAM
Spending $4160 every 3 years (possibly getting 4 years life but by
then figure on it costing us $6000 due to inflation) isn't so bad if
the mileage were something like 10,000 miles per year is a battery
cost of only 15~20 cents per mile in this hybrid VW van application
(plus the cost of recharging energy from hydrocarbon fuel and/or via
120 volt 20 amp outlet that'll recharge at 2 kw/hr and figure a
minimum of 6 hours if fully discharged or 3 hours at 50%, and we
should plan on paying $.25/kwhr.)
So, technically it's doable, but not by much, especially after
spending the extra twenty thousand on top of whatever the VW van or
SUV cost.
Wheel motors of rare earth magnets are not cheap, nor will the really
big alternator driven off the main gas or diesel engine be anything
off the shelf. The little computer and all the necessary controlling
circuits will be a given at perhaps $5000.