Long-life batteries from Dell and HP can keep laptops running for as many as 20 hours at a stretch. But you don't need a powerful external battery to get more use out of your current battery. There are several things you can do now to extract precious additional minutes from the basic six-cell battery found in most laptops.
Adjust only a few factors and you'll derive most of the available power savings. The biggest consumers of battery power are the screen, the processor, the optical drive, and the disk. Of these, the screen is by far the most important. It's also the easiest to adjust. Lower the brightness of the screen to the lowest level at which you can comfortably work and you'll have done more to save battery life than any other tweak can deliver.
The processor is frequently beyond your immediate control -- you've got to get the work done. However, eliminating background tasks such as listening to music or streaming video will lighten the processor's load. Similarly, keeping Wi-Fi use to a minimum can buy you significant time. When you have a choice, plugging in a network cable is much easier on your battery than wireless networking.
Optical drives are largely used for optional activities, such as watching DVDs, listening to CDs, or ripping music. These are all power-hungry uses. Since most of them can be postponed with little downside, avoid using the optical drive until you can plug in to a power source.
One component that does not consume much power is the hard disk. In fact, the widely accepted view that SSDs (solid-state drives) provide important power savings over mechanical drives is simply wrong. The power savings delivered by SSDs when compared with hard drives is minimal to nonexistent. Per various hardware vendors, an SSD adds only about 10 minutes of useful life to a battery charge. This fact shows just how far hard-disk technology has advanced: Despite relying on many moving parts, its power consumption runs even with a solid-state device. SSDs should be bought either to ruggedize a system or for performance benefits, but not for energy savings.
Some of these adjustments can be automated by using the power-consumption profiles that are set up by the various operating systems or hardware-vendor utilities. Many users choose one profile they feel suits them and never change it. However, changing profiles is easy to do and will conserve battery life. So if you know your current workload will stretch your battery's capacity, switch to a lighter, economy profile. And then switch back to your regular profile once you're fully charged.
Toggling power profiles will keep you from having to configure several components to stretch your battery life. Or simpler yet, consider one of today's long-life batteries.