Yes, there are kits available for some cars, VW Rabbit/Golf for
instance. See
http://www.electroauto.com - not the only seller of such
things but a good start.
To see a successful DIY effort, check out
www.kiwiev.com.
Most successful conversions that I have seen use lead-acid batteries,
but while these work OK, they do suffer from the twin problems of
weight and limited battery life (300 - 500 cycles).
Lithium-ion batteries are now starting to become more readily
available, Thundersky is one brand that looks very promising. Li-Ion
batteries offer less weight than lead-acid for the same capacity, and
if the manufacturer's claims bear out they should last for 2000+
cycles.
Performance of the converted car will depend on several variables,
mainly battery capacity and motor power.. A good performance envelope
to aim for is to get better than 100 kph (60mph) maximum speed, and to
be able to maintain that speed for better 1 hour on a charge.
