CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [372]
Nickel-Cadmium
Ni-Cds were the first batteries commonly used in mobile PCs, which means the technology was full of little problems. Probably most irritating was a little thing called battery memory, or the tendency of a Ni-Cd battery to lose a significant amount of its rechargeability if it was charged repeatedly without being totally discharged. A battery that originally kept a laptop running for two hours would eventually only keep that same laptop going for 30 minutes or less. Figure 21-26 shows a typical Ni-Cd battery.
Figure 21-26 Ni-Cd battery
To prevent memory problems, a Ni-Cd battery had to be discharged completely before each recharging. Recharging was tricky as well, because Ni-Cd batteries disliked being overcharged. Unfortunately, there was no way to verify when a battery was fully charged without an expensive charging machine, which none of us had. As a result, most Ni-Cd batteries lasted an extremely short time before having to be replaced. A quick fix was to purchase a conditioning charger. These chargers would first, totally discharge the Ni-Cd battery and then, generate a special “reverse” current that, in a way, cleaned internal parts of the battery so it could be recharged more often and would run longer on each recharge. Ni-Cd batteries would, at best, last for 1,000 charges, and far fewer with poor treatment. Ni-Cds were extremely susceptible to heat and would self-discharge over time if not used. Leaving a Ni-Cd in the car in the summer was guaranteed to result in a fully discharged battery in next to no time!
But Ni-Cd batteries didn’t stop causing trouble after they died. The highly toxic metals inside the batteries made it unacceptable simply to throw them in the trash. Ni-Cd batteries should be disposed of via specialized disposal companies. This is very important! Even though Ni-Cd batteries aren’t used in PCs very often anymore, many devices, such as cellular and cordless phones, still use Ni-Cd batteries. Don’t trash the environment by tossing Ni-Cds in a landfill. Turn them in at the closest special disposal site; most recycling centers are glad to take them. Also, many battery manufacturers/distributors will take them. The environment you help preserve just might be yours—or your kids’!
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EXAM TIP You must use disposal companies or battery recycling services to dispose of the highly toxic Ni-Cd batteries.
Nickel Metal Hydride
Ni-MH batteries were the next generation of mobile PC batteries and are still quite common today. Basically, Ni-MH batteries are Ni-Cd batteries without most of the headaches. Ni-MH batteries are much less susceptible to memory problems, can tolerate overcharging better, can take more recharging, and can last longer between rechargings. Like Ni-Cds, Ni-MH batteries are susceptible to heat, but at least they are considered less toxic to the environment. A special disposal is still a good idea. Unlike Ni-Cds, it’s usually better to recharge an Ni-MH with shallow recharges as opposed to a complete discharge/recharge. Ni-MH is a popular replacement battery for Ni-Cd systems (Figure 21-27).
Figure 21-27 Ni-MH battery
Lithium Ion
The most common battery used today is Li-Ion. Li-Ion batteries are powerful, completely immune to memory problems, and last at least twice as long as comparable Ni-MH batteries on one charge. Sadly, they can’t handle as many charges as Ni-MH types, but today’s users are usually more than glad to give up total battery lifespan in return for longer periods between charges. Li-Ion batteries will explode if they are overcharged, so all Li-Ion batteries sold with PCs have built-in circuitry to prevent accidental overcharging. Lithium batteries can only be used on systems designed to use them. They can’t be used as replacement batteries (Figure 21-28).
Figure 21-28 Li-Ion