The Chevrolet Volt claims up to 70 mpg what is the real number?

[Hankm1]

I would like to know the real comparison between a high mileage gasoline car and an electric or hybrid car.

It would include the cost and environmental impact of manufacturing exotic batteries and rare earth materials for the magnets in the motors. and the costs of the charger and electricity to recharge.
AND don't forget a sinking fund to pay for the crushing cost of replacing the battery pack every so often (they always conveniently forget this one)

 

[Breathonthewind]

What is a "real" number may depend upon what you want to consider. In an effort to increase the apparent mileage some of the volt advertising only counted the actual gasoline used and not the energy in any electrical charge. This is how they made the "outrageous" claim of 230 miles per gallon. They have since backed off this number and the marketing attempt is not to their credit. More recently they are claiming around 70 to 100+ miles to a gallon. While this is more reasonable and some test drives have determined that they were getting a combined gasoline/electric "mileage equivalency" of around 90mpg, the credit goes to the electric motor and not the petrol engine.

Tesla had calculated their electric drive train at over 6 times more efficient than a petrol engine.1 We say that a petrol engine is around 15% efficient but just starting out, standing in traffic or even in stop and go traffic it would probably be fortunate to achieve this. "Fuel efficient" cars are using the same tricks that an electric vehicle uses to extend its range: lighter vehicles, better aerodynamics, and less rolling resistance. What the gas vehicle does or cannot have is the more efficient drive train or regenerative braking.

So given the efficiency differences of the drive train if the average petrol vehicle gets around 20 mpg then the "average" electric vehicle should get about 6 times this or about 120 MPGe. Present electric vehicles are doing better than this.2

There are a number of ways to consider the cost of the battery pack. I would argue that you should not include it for the initial life of the original pack. When you buy a new electric car, you are paying for the battery pack. It depreciates until its useful life is gone in about 8 to 10 years. Both the Leaf and the Volt are warranty their packs for 8 years. To amortize the cost of a new pack over the initial miles is to consider the cost twice. For a bit of a rundown on the costs per mile you can take a look at my answer here.3 The "crushing cost" of a battery pack is presently down to approximately $9000 and you may be able to find a pack with double the range and half the cost before the warranty runs out: http://electric-vehicles-cars-bikes.blogspot.com/2010/05/nissan-say-leaf-ev-battery-pack-cost.html

Although you are asking for an analysis of battery chemistry's and motors these vary widely. The AC motor does not use rare earth magnets, there are many different battery chemistry's and technology is advancing rapidly. Ultracapacitors are already being used in some buses (4) as a means for energy storage and it is likely that they will increasingly be combined with some battery chemistry to produce a composite energy storage system.5 Such an extensive analysis would have to be compared to refinery pollution, transportation pollution, the overwhelming "oil spill" from improperly disposed of drain oil, gas station and highway run off each year.6

 

[DON'TPANIC]

The real number depends on how you drive it. If you use nothing but electricity, you'lll get the cost equivalent of 90 mpg (on peak rates), with normal driving (not babying it, NORMAL driving). With off peak rates (over night, when most of your charging is done) you get the cost equivalent of 135 mpg.

Of course in a few years gas will be more expensive and electricity will still cost the same, you will probably get the equivalent of over 200 mpg. If we lived in England, we would get the cost equivalent of 500 mpg today.

But if you want to only calculate for never plugging it in (wasteful) and only using gas for your energy, you would get about 35 mpg, city AND highway, which still ain't bad.

Plus there's tax credits to offset cost.