The Laptop Battery Guide February 1998 



The Laptop Battery Guide

Getting the most out of your batteries ... by Tom S. Bair Jr.

Many people who buy laptop computers tend to think that the included battery will last as long as the laptop itself. This is not true, and when the time comes to replace the battery, laptop owners find it isn't as easy -- or as inexpensive -- as replacing the batteries in a flashlight or even a wristwatch.

A Life of Its Own

The number one rule to remember is that all rechargeable batteries are designed to be used a certain number of times before they lose their ability to hold a charge. Most average rechargeable batteries will work for about two years, but that depends on the type of battery it is, how much you use it, and how well you recharge it.

So how do you tell when it is time to replace the battery? Manufacturers advise you to replace your battery when the current battery can only hold a recharge of 25 percent of its original capacity. If your battery used to last 2 hours and now only lasts 30 minutes, it's time for a new battery.

Some laptop users will carry two batteries to avoid a situation of not having power available to their laptop. To make this work effectively, however, you must remember to alternate the two batteries equally, else the backup battery will lose its ability to hold a charge due to long periods of inactivity.

Remember, too, that each time you recharge a battery, it will fail to return to the same level of charge it had reached on the last charge. Most batteries will reach 80-percent storage capacity within a few hundred charging cycles.

Nickel-Cadmium (NiCad)

NiCad batteries have faded out of use due to improvements in battery technology. Until two years ago, however, they were the most commonly used rechargeable laptop battery. They are still used as replacements in older laptops, but newer portables don't use them.

A NiCad battery has several drawbacks, the most annoying being that its length of use between charges is less than two hours. NiCad batteries are also heavier than other batteries, and have a high toxicity effect on the environment when discarded. Finally, NiCad batteries suffer from an affliction known as the "memory effect." The battery will only charge to the level at which the battery was last discharged, due to an accumulation of gas bubbles on the cell plates. If a battery is discharged to 30% and then recharged, the battery will only charge to 30% of its capacity, thus shrinking the battery's "gas tank."

The best way to eliminate the memory effect and remove the accumulated gas bubbles on the cell plates is to "burp," or condition your NiCad battery. This means draining or fully discharging the battery until your laptop shuts off, and then recharging it. Remember, however, not to leave the battery on the charger for extended periods of time; this can cause the cells to heat up and will quickly ruin the battery.

NiCad batteries have a life of 500 to 750 recharges, depending on memory effect. The only advantage of the NiCad compared to other laptop batteries is its low price -- but keep in mind that you get what you pay for.

Nickel-Metal Hydride (NiMH)

NiMH batteries offer several improvements over NiCad batteries. They can be used in most all laptop computers built during the last five years, they have a slightly longer life cycle between charges, they are lighter, and they contain no toxic Cadmium. They are also known as the memory free battery which offers higher capacity. MiMH batteries suffer less from the memory effect and have 30% longer run times. On the down side, they're more than NiCad batteries.

The life span of NiMH batteries isn't as long as NiCad batteries, lasting only about 250 to 500 charges. Older laptop computers can use either NiCad or NiMH batteries, while the newer laptops will use either NiMH or LiIon batteries. Check your owner's manual to see which type battery you can use.

The first several times that you charge your new Nickel Metal Hydride battery, trickle charge (slow charge) it, this will "form" the cells. The NiMH battery can withstand random charging. However, you need to avoid overheating the battery; heat is a NiMH battery's worst enemy. Also, do not allow your battery to sit dormant for extended periods of time without charging, because the cells will lose their ability to hold a charge.

Lithuim-Ion (LiIon)

The newest laptop battery on the market is LiIon, which has been around for a bit more than a year. They are the lightest batteries yet made, and they have a life cycle between charges of up to four hours. They don't even suffer from memory effect.

It is uncertain as to the life span of a LiIon. Estimates so far put it at about five years, or as much as 1,200 recharges. The only drawback to these powerhouse batteries is their price, as much as $400 -- but as with all other computer items, this price is expected to drop as time goes by. Currently, LiIon batteries are hard to get due to the inability of suppliers to meet the large demand for them. Of course, if your laptop comes with a LiIon battery, the replace cost should be considerably by the time you need to replace it, several years from now.

Future Trends

Next in line to be developed are Zinc Air and Lithium Polymer batteries. We should see Lithium Polymer on the market by mid-1998. The greatest advantage of these batteries is their ability to easily conform to any shape or size, allowing laptops to be further streamlined in the future.

Battery Tips

I suggest that to extend battery life laptop owners follow five rules:

  1. Do not expose your battery to heat. Permanent damage will result if the battery is exposed to temperatures above 110 F or 43 C. Leaving your battery inside a car in the hot summer sun is an obvious example.

  2. Do not over-charge your battery. Disconnecting and reconnecting your computer to AC power frequently, without discharging the battery, causes over-charging. This applies to NiCads only, since NiMH batteries can accept random charges frequently.

  3. Do not over-discharge the battery. Your laptop consumes battery power even when it is turned off. If you do not use your laptop for extended periods of time, a week or more, remove the battery pack from the laptop. Store batteries in a cool, dry place away from heat and metal objects. Batteries left idle for extended periods of time will self-discharge. Remember to charge them again before using them.

  4. Charge battery packs for 12 hours when they are new. Laptop batteries are completely discharged at the time of purchase, and need a full charge before their first use. To increase the life of your batteries, don't leave them dormant for extended periods of time. Even if you use AC power most of the time, use the battery periodically to keep it fresh and healthy. Unplug your AC adapter when the computer is not in use.

  5. Attempt to use your laptop in room temperature. The battery operating time between recharges decreases as the temperature decreases. The best operating room temperature is between 60° and 72° F.

Recycle When They Die

Please be kind to the environment and do not throw your batteries in the trash. The EPA estimates that 200 tons of cadmium and 260,000 tons of lead enter the waste stream annually. For safe recycling please send your old batteries to


1-800-Batteries
Attn: Recycling Dept.
14388 Union Ave.
San Jose, CA 95124-2815

Tel (408)879-1930
Fax (408)879-1969

These people will make a very small profit recycling the useable components in your battery, safely disposing of what is left. It is a nasty job, and they are making just above a break-even point of profit to help keep our environment safe. I highly recommend using them for disposing of old batteries.


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