A laptop battery should be small and lightweight, but it should also last as long as possible between charges. Unfortunately, longer-lasting batteries are usually heavier than the ones that need more frequent recharges, so the ideal battery provides a balance between operating time and weight.
Most new laptops use lithium-ion (Li-ion) batteries, which are more costly than older nickel-cadmium (NiCad) and nickel-metal-hydride (NiMH) types, but they offer several advantages:
They carry more energy in the same space.
They weigh less than older types.
They don't require periodic discharge.
Some laptop models can accept two different battery packs: one with six battery cells that can last up to two or three hours on a charge, and larger nine-cell packs that extend the battery life by several hours. The larger (and heavier) nine-cell battery packs may be worth the extra expense if you want to use your laptop on coast-to-coast or transatlantic flights.
Another approach to extending the battery life is used in laptops with a modular drive bay that can hold a second battery in the space that normally holds the DVD drive. With both batteries in place, the computer can run for almost twice as long, and it's not necessary to suspend the system to replace a battery.
The other way to extend a computer battery's life is to reduce the amount of power the computer demands. Therefore, the battery in a computer with a slower CPU or a smaller screen lasts longer.