pertaining to hybrid electric vechicles, i want to know what is the
benifit if any to using prizmatic type nickle metal hydride batteries,
as appose to the standard cylindrical type.  I know that the Honda
Insite uses the standard clindrical type Ni-Metal hydride battery but
the Toyota Prius uses the prizmatic.  I was told that the prizmatic
version was better but they were not sure why.  hopefully you can
shine some light on the matter.  thank you.

"Batteries 101" [ http://www.rahq.com/images/batteries_101/Batteries_101.htm
], about 2/3 the way down the page, states that most battery sizes are
created for OEMs (original equipment manufacturers) that require a
standard size of battery that can be produced in quantities of
millions. On the specific subject of rectangular prismatic cells for
NIMH batteries they say "A limited range of rectangle-shaped, or
prismatic cells are available in NiCd and NiMH chemistries.  Again,
the reason for the existence of these cells relates to size and form
factors that were required by original equipment manufacturers."

The raindrop laborotories web site has an article on Zero emmision
vechicles [ http://216.239.39.100/search?q=cache:MAMD2oO1rf0C:www.rdrop.com/ev/hybrid.pdf+Prismatic++vs+cylindrical+nimh+batteries&hl=en&ie=UTF-8
] (html version) or [ http://www.rdrop.com/ev/hybrid.pdf ] (pdf
version) compares the most common type of cylindrical and prismatic
batteries used in electric cars. The prismatic cell had much higher
energy density and total electrical capacity, but the cylindrical cell
had the lower overall size and weight. Specifically, the prismatic
type had about 50% higher energy per kg, and about 3 times as much
total power.

So basically, the prismatic type of cell is superior in general, since
you can pack more juice into each pound of material. The cylindrical
cells are sometimes used because their total weight and size is lower,
allowing for a lighter smaller vehicle albiet with less overall range.

I actually own stock in the company that makes the prismatic type of
battery (the ovonic battery), which from my understanding is having
some issues with patent licensing and infringement problems and is
having manufacturing trouble as well. Therefore, although the
prismatic type ovonic battery is better overall, the cylinder type may
be used because it is easier to obtain, with fewer licensing hassles.

I believe you will find that both of the batteries described are
Nickel-Metal Hydride (NiMH), and that the Prismatic is more compact,
while the cylindrical is bulkier, and that the cylindrcal variety
offers a slightly higher Wh/kg.