Laptops are powered by several different types of batteries. These batteries provide direct-current power to your laptop.
Lithium-ion: This is the type of battery you want to have in your laptop. This type is lightweight and performs better than the other types of batteries. Unlike NiCad or NiMH batteries, lithium-ion batteries don’t have the dreaded “memory effect.” The memory effect is the property of nickel-cadmium batteries that causes them to lose their capacity for full recharging if they are discharged repeatedly the same amount and then recharged without overcharge before they have fully drained. There’s usually a rapid-charging option with lithium-ion batteries, which is good when you’re in a time crunch. Finally, this type of battery is more environmentally friendly than the other types.
Two older types of batteries, once popular in portable computers, are nickel-cadmium (NiCad) and nickel-metal hydride (NiMH). The NiCad isn’t often considered for laptops these days because it suffered unpleasantly from The Dreaded Memory Effect. A NiMH battery is longer lasting than a NiCad, but it too woefully suffers from The Dreaded Memory Effect.
You can confirm which type of battery your laptop has by looking at its label. See the next section.
A few laptop computers out there are still using NiMH batteries. This is fine, of course, but you might want to check to see whether you can find a battery upgrade to the Li-ion type.
To prolong the life of a NiMH battery, I recommend fully discharging it every so often. For example, after you use, drain, and recharge the NiMH battery about four times (or so), do a complete drain and then recharge it again. That should help the battery last a bit longer.
Your laptop might have two additional batteries inside. A secondary, alkaline battery inside is used to power the laptop's internal clock. An optional third battery keeps things powered for the minute or so that it takes you to swap out a spent main battery with a fresh one. See the section "Love that spare battery," later in this chapter.
Using unapproved batteries in your laptop may lead to bad situations, such as, oh, the laptop catching fire and exploding. If you doubt me, look up exploding laptop on YouTube.