There are three types of cheap laptop battery chemistries. Nickel cadmium was the first chemistry, then follows nickel metal hydride and lithium ion.
NiCd batteries were the first rechargeable batteries for notebook computers and characterized in low cost, versatility and high output current capability. NiCd batteries can be charged quickly and applied in a wide range of products. However, they are now not used in notebooks because of the newer and higher power NiMH and LiON batteries.
Nickel Metal Hydride (NiMH)
NiMH batteries are a significant improvement over NiCd batteries in cost, safety, reliability and capacity. Currently the most widely used notebook battery, the NiMH battery has only one drawback. The "memory effect" of NiMH batteries requires that they be fully discharged prior to recharging for maximum charge effectiveness.
Lithium Ion (LiON)
LiON batteries are now the most popular notebook battery because of improvements over NiMH in the area of memory effect. Moreover, for batteries of comparable capacity, LiON batteries are generally lighter in weight than NiMH batteries. Because the LiON chemistry is the newest in the market and have these advantages, LiON batteries is often much more expensive than for NiMH batteries with the same actual capacity. Dell Inspiron 1545 uses this kind of battery, and the battery life is quite good.
Smart / Dumb Batteries
Some batteries are referred as "smart" or "dumb." Smart batteries have internal microprocessor circuits which help manage battery energy, indicate the state of the charge, forecast running time and track battery usage. Dumb batteries do not have these smart battery functions.