NYU COMPUTER STORE

Getting the Most out of Your Laptop's Batteries

by Kevin J.Edwards

[Ed: Links to web pages and/or e-mail addresses which have become inactive since the publication of this article have been enclosed in curly brackets { }. Replacement links have been provided where possible.]

Summer is upon us, and for many of us that means travel -- and portable computers. If you'll be traveling with a portable computer, there are several steps you should take for maximum battery life:

--use power-management software
--avoid using backlighting, hard drives, and floppies when you don't need them
--charge and maintain your batteries properly on Macintosh PowerBooks, turn off AppleTalk when it's not in use.

Older portables, including the Mac PowerBook 100, used lead-acid batteries. Nowadays, two other types of batteries are more common -- nickel-cadmium (NiCad) and nickel-metal hydride (NiMH) -- and a third, lithium-ion, is coming into use. NiCad batteries -- the same sort that's used for most rechargeables -- are more common but have a couple of disadvantages: the use of toxic cadmium, and the memory effect, which I'll discuss in a moment. NiMH and lithium-ion batteries avoid these problems, but are more expensive and thus less common.

Lead-Acid Batteries

If you have a notebook with a lead-acid battery, make sure to keep the battery charged. These batteries don't suffer from memory effect, but they can suffer from being drained too low. Once a lead-acid battery has drained too low, it will be unable to be recharged. If you will be storing a notebook with a lead-acid battery, make sure that it is fully charged, and recharge it every three to six months.

Charging a New Battery

The manufacturers recommend that all new PowerBook and IBM ThinkPad model batteries be charged for about twenty-four hours before their first use. The user's manual of any new notebook computer will describe proper procedures for its battery; it pays to follow those instructions carefully. You can use the notebooks while they are charging; however, this increases the amount of time needed for a full charge.

Recharging and the Memory Effect

For most notebooks, it takes a full eight hours to recharge the battery completely. The battery can charge about 75 percent in about an hour; the last 25 percent goes much more slowly. Be sure to check the manual for your model's charging time. It's important to let the battery drain completely before starting to recharge. The habit of recharging a battery that is not fully drained will cause it to lose its charging capacity; it will act as if it's been discharged when it reaches the level it was at before the last recharging -- the memory effect. You can reduce the memory effect slightly by reconditioning the battery -- completely discharging it, and then fully recharging it. Keep in mind that your battery likes to be drained completely and recharged completely. The worst thing you can do to the battery is to drain it and leave it drained, or habitually to recharge it before it has fully drained.

Batteries and AC Adapters at Home

Many owners of notebook computers keep them at home on their desk. There is nothing wrong with leaving your PowerBook plugged in all the time; you can even leave it on, in sleep mode.

However, you would want to drain the battery occasionally. If you know that you'll be using your computer for a couple of hours, unplug it, and run it off the battery until it drains. Then, plug it back in. On the other hand, if you won't be using it, turn it on and let it drain completely before plugging it back in. Try to do this at least once or twice a month.

A few notebooks have peculiar rules about being used without a battery installed, or when you can install a battery. The PowerBook 150 can be used from its AC adapter without a battery -- but be careful: you must have the adapter plugged in before installing a drained battery. Inserting a fully drained battery in a PowerBook 150 before plugging in the adapter can cause a fuse on the logic board to blow.

If you will be storing your PowerBook for a couple of months or more, charge the battery completely, and then unplug the adapter and remove the battery from the PowerBook. When you get back, the battery will have drained on its own after about a month. This is normal for NiCad batteries.

On the Road

If you leave a battery inside your PowerBook 150 while it's unplugged, it will drain much faster than if you remove it. It will drain even faster if your PowerBook is in sleep mode -- perhaps in a couple of days.

If you leave a drained battery inside the PowerBook 150, you will corrupt the PowerManager. The PowerManager is the part of the computer that coordinates where the power is going to and coming from. If it gets corrupted, your PowerBook will not turn on until the PowerManager is reset. The only way to reset the PowerManager is to open up the PowerBook, which requires an authorized Apple Service Technician. Make sure to either remove the battery, or leave the PowerBook plugged in.

When traveling with your notebook batteries uninstalled, make sure that their contacts are covered by something that is nonconductive. Exposed contacts can be shorted by a paper clip, coin, or other conductive material that is loose inside the carrying case -- and that, of course, will drain your battery. Many batteries come with covers that slide over their contacts; make sure to use them.

Intelligent Batteries and the PowerBook 500s

The batteries of the PowerBook 500 series computers are "intelligent" which means they contain a microprocessor that monitors the battery's status. The system software can thus tell you how much time is left and whether the battery is charging. The 500 series PowerBooks don't automatically perform a deep discharge of the batteries before recharging them, nor is a deep discharge recommended. Deeply discharging an intelligent battery would cause the voltage to dip below the level needed for its processor to perform properly.

The recommended procedure is to use the PowerBook on battery power until the battery-level warning dialog box is displayed; at that point, be sure to save any files that you are working on, since you may not be able to save them later. Continue to use the PowerBook until the unit goes to sleep automatically, then connect the AC adapter and fully charge the batteries. You should do this every three months or so.

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Kevin J. Edwards was the Service Manager for the NYU Computer Store at the time of this article's publication.
{edwardsk@acfcluster.nyu.edu}

Posted 25 October 1995. Revised 20 May 2004.