8. Battery

The most important feature of a notebook is its mobility. Rechargeable batteries supply the power of the notebook. Like everything in the IT business there are several different options from cheap and heavy to expensive and light.

The most common rechargeable batteries being used in a Notebook are:

Nickel-Cadmium (NiCad) Nickel-Metal Hydride (NiMH) Lithium-Ion (Li-Ion)

	Ni-Cad	Ni-MH	Li-Ion
Energy Density (W-Hr/kg)	40	60	90
Energy Density (W-Hr/l)	100	140	210
Operating Voltage	1,2	1,2	3,6
Lifetime (approx. Cycles)	1000	800	1000
Self Discharge	15%/month	20%/month	6%/month

Ni-Cad/Ni-MH

In budget notebooks you will find Ni-Cad or Ni-MH batteries. The price difference to Li-Ion is about US$30. But wait before you start running to the next computer shack to get a Li-Ion battery pack. You should continue reading this portion of the article, because there are major differences between Ni-Cad, Ni-MH and Li-Ion batteries.

Ni-Cad and Ni-MH batteries are charged with a constant current . The charger monitors the battery voltage and temperature. It is looking for a rise of the battery voltage that usually occurs at the end of the charging cycle. Ni-Cad and NiMH have similar behavior except for the point close to the end of the charging process.

The temperature of NiMH batteries rises faster than 1°C/minute once the battery has reached the end of its charging cycle.