cooling system installed to prevent thermal degradation. At this point, it is unclear whether all of
the battery types described below can provide half the rated peak power for several minutes, as is
required for a hill climb.
Life can be based on both calendar years and charge/discharge cycles. USABC has set mid- and
long-term goals of 5 and 10 years and 600 and 1,000 cycles respectively. Conventional lead acid
batteries in electric car use have a life of only about two to three years and 300 to 400 cycles. For
some batteries, calendar life and cycle life may present different limiting constraints, and the life
itself is affected by how deeply a battery is discharged.
There are several other parameters that are of major concern, such as the power density and
energy density, which are measures of battery power and energy storage capabilities on a
volumetric basis (to avoid very large batteries), power and energy degradation over the useful life,
fast recharge time, range of ambient operating conditions, maintenance requirements, and
durability. USABC goals for some of these parameters are shown in table 3-10. In addition, there
are special concerns with each battery type that include behavior at low charge, special charging
characteristics, and recyclability. This review of batteries is not meant to be comprehensive nor
intended to cover all of the above factors. Rather, the intention of the review is to describe
automanufacturer concerns and battery manufacturer inputs on the current status of battery
development, while the conclusions reflect only OTA’s opinion on battery prospects.Credible specification of battery parameters is critical to judging EV capabilities, but in fact
such specification is difficult to come by. Measuring battery parameters raises many issues, as the
results are sensitive to the test procedure and ambient conditions employed. For example, most
batteries display reduced energy densities at higher power levels, as well as during cyclically
varying power draws (as will be the case in an electric vehicle). Yet, specific energy values
generally are quoted at a constant discharge rate that would drain the battery in three hours (c/3).
As noted, many batteries also display significant reductions in power density at low state-of-
charge, and at reduced ambient temperatures, while available data may be for filly charged
batteries at 20oC. Finally, battery characteristics are often different among single cells, modules,
and collections of modules required for a high-voltage battery. In many battery types, the failure
of a single cell, or variations (owing to production tolerances) between cells often has significant
impact on battery performance.Auto manufacturers interviewed by OTA universally agreed that many battery manufacturer
claims about battery performance and longevity are unlikely to be reproduced in a vehicle
environment. European manufacturers have devised new testing procedures through their joint
consortium, EUCAR, that appear to be more stringent and comprehensive than those performed
previously by USABC or by DOE affiliated laboratories;^68 similarly, USABC in 1994 also revised
its testing procedures, which are now reported to be very stringent. Auto manufacturers stressed
the need to test an entire high-voltage battery system with the thermal and electrical management
systems included as part of the overall system to obtain a good picture of real-world performance.