The main difference between the two is that NiMH battery
(the newer technology of the two) offers higher energy density than NiCads.
In other words, the capacity of a NiMH is approximately twice
the capacity of its NiCad counterpart.
What this means is for you is increased run-time from the battery
with no additional bulk or weight. NiMH also offers another major advantage:
NiCad batteries tend to suffer from what is called the "memory effect".
NiMH batteries are less prone to develop this problem and thus require
less maintenance and conditioning. NiMH batteries are also environmentally
friendlier than NiCad batteries since they do not contain heavy metals
(which present serious landfill problems). Note:
Not all devices can accept both NiCad or NiMH batteries.
Lithium-Ion (Li-Ion) has become the new standard for portable power
in consumer devices. Li-Ion batterys produce the same energy as NiMH
battery but weighs approximately 20%-35% less. This is can make a noticeable
difference in devices such as cellular phones, camcorders or notebook
computers where the battery makes up a significant portion of the total weight.
Another reason Li-Ion batteries have become so popular is that
they do not suffer from the "memory effect" at all. They are also
environmentally friendly because they don't contain toxic materials such
as Cadmium or Mercury.