Battery novices often argue that advanced battery systems
are now available that offer very high energy densities, deliver
1000 charge/discharge cycles and are paper thin. These
attributes are indeed achievable — unfortunately not in the
same battery pack. A given battery may be designed for small
size and long runtime, but this pack would have a limited
cycle life. Another battery may be built for durability, but
it would be big and bulky. A third pack may have high energy
density and long durability, but would be too expensive for
the commercial consumer.
Battery manufacturers are well aware of customer needs and
have responded by offering battery packs that best suit the
specific application. The mobile phone industry is an example
of this clever adaptation. For this market, the emphasis is
placed on small size and high energy density. Longevity comes
in second.
The mention of NiMH on a battery pack does not automatically
guarantee high energy density. A prismatic NiMH battery for
a mobile phone, for example, is made for slim geometry and
may only have an energy density of 60Wh/kg. The cycle count
for this battery would be limited to around 300. In comparison,
a cylindrical NiMH offers energy densities of 80Wh/kg and
higher. Still, the cycle count of this battery will be moderate
to low. High durability NiMH batteries, which are intended
for industrial use and the electric vehicle enduring 1000 discharges
to 80 percent depth-of discharge, are packaged in large
cylindrical cells. The energy density on these cells is a
modest 70Wh/kg.
Similarly, Li-ion batteries for defense applications
are being produced that far exceed the energy density of the
commercial equivalent. Unfortunately, these super-high capacity
Li-ion batteries are deemed unsafe in the hands of the
public. Neither would the general public be able to afford
to buy them.
When energy densities and cycle life are mentioned, this
book refers to a middle-of-the-road commercial battery that
offers a reasonable compromise in size, energy density, cycle
life and price. The book excludes miracle batteries that only
live in controlled environments.
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