Matching Electric Vehicle Battery Performance to User Needs

The range of electric vehicles (EVs) is inherently limited by the energy content of the batteries. This important and obvious limitation has caused EV battery development to become focused on batteries having the highest possible specific energies (i.e., Wh/kg). When the actual driving and buying habits of the motoring public are considered, however, it can be seen that most EV batteries are more deficient in power than in energy. Although many EV batteries can satisfy the necessary energy requirements for a viable EV, few are likely to satisfy the power needs, especially when cost is considered.

This study presents an analysis of the battery power requirements based upon the characteristics of current automobiles actually purchased by the U.S. motoring public, and the energy requirements based upon actual commuter driving distances in Southern California. The conclusions of the study are that ( 1 ) separate considerations of battery specific energy, specific power, and cost are inadequate to define a commercially viable EV battery, and (2) the battery power/energy (P/E) ratios currently being considered by EV automakers are too low. Low P/E ratios result either in an expensive battery or in low vehicle performance, either of which will be unattractive to potential buyers of electric automibiles. A recommended battery specification is presented which should be satisfactory for a commuter EV satisfying 90% of the Southern California market.