http://en.allexperts.com/q/Science-Kids-3250/Hamster-Power.htm
according to the site a hamster should be able to put out 150mA @ 3V, this equates to 0.45w, you need 85kWh to charge the battery. this means that....
Full charge from dead will take = 21 Years of consistent output
Top off charge for the day (lets say you drive 40km per day, 7.5kWh) = 1.89 Years.
that obviously takes too long so if you have a hamster power farm of 500 generators you could charge your car from dead in 15.7 Days!
not bad at all....