The 30 percent value is an optimistic number for current technology, since every one of the
components have been selected to be at the 2005 expected values, which are higher than the
actual observed range. It also assumes the availability of a semi-bipolar battery that can produce
high peak power for acceleration. It is easy to see that in the absence of such high peak-power
capability, fuel economy drops precipitously. If a normal lead acid battery with a peak-power
capability of 125 W/kg is used, composite fuel economy is only 24.5 mpg, which is almost 12
percent lower than the conventional Taurus! These findings are in good agreement with the
observed fuel efficiency of some HEVS with conventional lead acid batteries. As noted, both
Nissan and BMW reported lower fuel economy for their series hybrid vehicles, even though they
used nickel cadmium batteries with specific peak power of 125 to 150 W/kg.
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