Many competing factors enter into the choice of a specific laptop: weight, size, price, battery life, expandability, and so on. Of these, battery life is rarely a primary concern until the system is actually purchased. The unspoken expectation is that standard batteries will get 3 to 4 hours of useful life from a single charge, while batteries with more cells can add a couple of hours of working time to this number.
This general rule, which has been valid for several years, is being challenged by new battery technology that can significantly extend productive time on today's notebooks. The newly extended window has an important consequence for a purchasing factor that is material to all users: the laptop's weight. If a battery can carry a system through an entire business day and beyond, then there is no longer any need to lug the power supply and cables in a roller bag or briefcase. This benefit is slightly tempered by the added weight of the batteries themselves.
[ Get tips for squeezing more life out of your battery. Download InfoWorld's InfoCountdown benchmark to measure the battery life of your laptop. ]
This article discusses several extended-life battery models available on standard notebooks and the kind of performance you can reasonably expect. The good news is that some batteries can carry you for well past 15 hours of work on a single charge.
Systems and batteries
To perform this evaluation, InfoWorld approached Dell and Hewlett-Packard to provide us with notebooks that represent typical professional models and to supply their corresponding long-life batteries. We specifically asked that they not make any extraordinary configuration changes to the systems to extend battery life for our tests. Ultimately, I examined a Dell Latitude E4300 with a "battery slice" and HP EliteBook 6930p laptop with two models of long-life batteries.
It's important to note that we asked for models with substantially different configurations (processor, operating system, capacity, etc.) so that we could obtain multiple data points. As a result, the numbers should not be used for comparing models, because there is no established baseline in common. Rather, the numbers should provide insight into what kind of battery life you can expect for recent laptop models.
The benchmark jungle
Industry benchmarks for laptop battery usage are a mixed bag. Different vendors use different measures, including JEITA (Japan Electronics and Information Technology Industries Association), Mobile Mark, and combinations of the two. Typically, these benchmarks involve measuring battery usage in a near-hibernation state, then at various levels of activity, and averaging the results. The problem is that users have no way of knowing the extent to which this average corresponds to their own usage profile. As a result, consumers end up viewing the numbers in the same way they do U.S. mileage figures for automobiles: as a generous overestimate that cannot be reproduced except in laboratories.
To avoid this mess, I decided to write a simple Java program that would simulate a light load. The program, InfoCountdown, runs continuously, writing the current and elapsed times to the screen and to the disk every 10 seconds. This generates a regular, intermittent disk and screen I/O operation. I configured the notebooks so that the screen was permanently on, the screen saver was disabled, and hibernation was turned off. Hence, the timings should represent the maximum battery life for very light but continuous work.
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