sodium-sulfur battery is illustrative. Early prototype batteries were available during the late- 1980s
and tested by Mercedes and BMW. These prototypes had a calendar life of about six months and
were plagued by excessive failures. Second generation prototypes were supplied to BMW and
Ford, and these doubled calendar life to about one year. More recently, two of the Ford Ecostar
vehicles have reported fires during charging. ABB is currently providing third generation
prototypes to Ford, but even these are not considered production ready. ABB is willing to
guarantee a calendar life of only one year in EV services for its latest sodium-sulfur prototypes,
although actual life may be two to three years.^87
Although the sodium-sulfur battery may pose especially difficult development problems, such
experiences are reported even for advanced lead acid batteries whose basic principles have been
utilized introduction batteries for many decades. INEL reports that the Sonnenschein advanced
lead acid battery has demonstrated very good cycle life in the laboratory, but that its in-use
reliability is very poor.^88 Once a battery has moved beyond the single-cell stage, manufacturers
estimate that a minimum of three years per stage is required to move to the module, prototype
battery, and preproduction battery stages, and a total testing time of nearly a decade will be
necessary for a proven production model.This estimate of time assumes that problems are successfully tackled in each stage and that
manufacturing processes can replicate cells with very little variability in mass production--an
assumption that remains unproven for almost all advanced battery types demonstrated to date.
Based on this, it is reasonable to conclude that batteries whose status is listed “3” in Table 3-12
will not be mass produced until 2000 at the earliest.^89
Vehicle lifetime costs depend on the battery durability, an issue about which little is known
except for the fact that usable lifetimes are quite different for different batteries. It should be
noted that battery life depends on the desire of the battery system and its usage pattern. Also,
there are tradeoffs between battery life and cost, specific energy, specific power, and user
specification of end-of-life criteria. For example, a battery may have very different “life,” if the
end-of-life criterion is set at 90 percent of initial energy density, or is set at 80 percent.
Nevertheless, for almost any set of reasonable criteria for end-of-life that are acceptable to auto
manufacturers, there are currently no advanced batteries that have demonstrated an average five-
year life in the field, nor have any battery manufacturers been willing to warranty a battery for this
period. Hence, even the prospect of five-year life in customer service is unproven and is an input
assumption for most analyses of battery costs.
Cost per kilowatt-hour of storage capacity in table 3-9 is based on production rates of at least
10,000 modules per month and are estimated from the educated guesses of battery manufacturers,
(except for the nickel-metal hydride battery where the cost controversy was noted earlier). The
cost estimates in the table are based on both battery and auto manufacturer inputs. Although OTA
has attempted to include only estimates that appear realistic given current knowledge, these
estimates may still be unreliable as most battery types are not yet production ready.(^8788) M.L. Shemmans,ABB, personal communication, December 1994.
EUCAR, see footnote 68.
(^89) California requirements for 1998-1999 can be met with pilot production as the total sales requirements are low. The ZEV mandates have been
adopted by New York and Massachusetts, however.