What is the different of Ni-Cd, Ni-MH and Li-ion?

Batteries in portable consumer devices (laptops and notebooks, camcorders, digital camera, etc.) are principally made using either Nickel Cadmium (Ni-Cd), Nickel Metal Hydride (Ni-MH) or Lithium Ion (Li-ion) technologies. Each type of rechargeable battery technology has its own unique characteristics:
Ni-Cd and Ni-MH: the main difference between the two is the fact that Ni-MH batteries (the newer of the two technologies) offer higher energy densities than NiCads. In other words, pound for pound, Ni-MH delivers approximately 100% more capacity than its Ni-Cd counterpart. What this translates into is increased run-time from the battery with no additional bulk to weigh down your portable device. Ni-MH also offers another major advantage: NiCad batteries tend to suffer from what is called the "Memory Effect". Ni-MH batteries are less prone to develop this dreaded affliction and thus require less maintenance and care. Ni-MH batteries are also more environmentally friendly than their Ni-Cd counterparts, since they do not contain heavy metals (which present serious landfill problems).Li-ion has quickly become the emerging standard for portable power in consumer devices. Li-ion batteries produce the same energy as Ni-MH batteries but weigh approximately 35% less. This is crucial in applications such as camcorders or notebook computers, where the battery makes up a significant portion of the device's 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 better for the environment because they don't contain toxic materials such as Cadmium or Mercury.