Reprinted with permission of Mobile Computing & Communications and Emap-Petersen. Rich Malloy offers insights on technical issues involving portable computers and communications devices. He is director of CFG Technical Labs, CurtCo Freedom Group's in-house testing facility.

Battery endurance is a crucial - if not the major - factor for those who travel a lot. The problem is that many notebook purchasers don't pay enough attention to battery endurance until after they have signed on the dotted line. In fact, for many users it is only after some outrageous mishap occurs that battery endurance attains its rightful place in the hierarchy of notebook features.

Usually this event has something to do with the notebook in question dying right in the middle of a crucial sales presentation or as a career-making memo is being written.

A lucky handful of notebook users have been pleasantly surprised at how long their notebooks can last between charges. For example, who could be disappointed by the Micron Go-Book2, which can last about 7 hours with its secondary battery slab attached?

For the rest of us, however, the news is usually not so rosy. And since the battery options for notebooks are few, if not nonexistent, our challenge is to find ways to stretch battery life for as long as possible.

Power-Management Options

The first thing to look at is the power-management parameters on the notebook. Most offer four basic settings: Maximum Power Savings, Maximum Performance, Customized and Disabled.

The optimal setting always represents a compromise between battery life and computer performance and is often a matter of personal style. Yes, the Maximum Power Savings setting will stretch battery endurance, but at a price. Some users, after taking some time to think, get disturbed when their screens suddenly black out after a few minutes of inactivity.

Others dislike waiting for their hard drives to rev up every time they click on an icon. To get more work done, many users will actually decrease power savings to avoid these delays.

How much do the power-management settings matter? To find out, we performed some battery tests. The Gateway Solo 5150 running at 300MHz offers a good combination of power and battery life. Its battery rating with our standard settings of 3 hours 35 minutes is well above average, and its Phoenix BIOS is typical of that in many notebooks.

We ran our PowerHour battery-endurance test at both Maximum Performance and Maximum Power Savings settings and found only a 16-minute difference between the two settings. Our suggestion is to run a customized level with all the parameters set midway between the two power extremes. This will likely provide good battery endurance without any onerous inconveniences.

Many users do not realize that there are additional adjustments on a notebook that can greatly affect battery life. The most prominent is the screen's backlight. Although it seems obvious, some users forget that by simply turning down the display's brightness, a screen will remain readable but will contribute to a significantly longer battery life.

To measure the effect of screen brightness, we performed a battery test at maximum brightness, minimum brightness and a value midway between the two extremes. The difference in battery life between the maximum and minimum brightness levels amounted to only about 20 minutes. Interestingly, the medium brightness level - our standard for lab testing - provided almost the same battery life as the minimum brightness level.

Note that when we looked at the screen, we could not see much of a difference between any of these brightness levels. Even our light meter showed a difference of only 8 percent between medium and maximum brightness settings. Thus, at the medium level we were getting pretty much the best of both worlds: a screen that was almost as bright as it could be, with very little detriment in battery endurance.

Closing the IR Window

Another significant way to save power is to disable the infrared (IR) port, particularly if this is something you rarely - if ever - use. If the IR window is enabled, it will send a signal every three seconds, looking for another IR device.

In our tests on the Solo, we found that leaving the IR window enabled would rob us of almost 30 minutes of battery life. To disable the IR window, double-click on the Infrared control panel, click the Options tab on the Infrared monitor, and uncheck the Enable box. You can always re-enable Infrared when you need.

Some users report that turning off the low-battery alarms on their notebooks will save 10 to 20 minutes of battery time. On the Solo, which has a modest alarm, this ploy had no effect. If your notebook has a loud, persistent and annoying alarm, however, disabling it may help. If it doesn't extend your battery endurance, it will at least make your seatmates on the plane happier.

Do PC Cards waste power even when they are not being used? On our test Solo, we inserted a Xircom 33.6Kbps modem and an IBM 10Mbps Ethernet LAN card before a battery test. Consequently, endurance was diminished by almost 10 minutes. But removing a PC Card increases the risk of losing or damaging it. Most users would simply be better off by leaving the PC Cards in the slot.

This behavior is not restricted to notebooks, however, because tests with a Dauphin Orasis tablet show that attaching a keyboard trims about 30 minutes from the battery endurance. But in today's multimedia world, the big question is how a DVD-equipped notebook does while playing a full-length, high-resolution movie. A DVD-equipped Solo 5150, lasted 2:12 while watching a movie, which is more than an hour short of its maximum - but, fortunately, long enough for most movies.