The problem is that this is not how people use their laptops in real life

A good example is people who use their laptops for viewing DVDs on an airplane flight. This is one of the more consistent battery drawing tasks that one can use on their laptop. Thus, a battery life claim of four hours might net just two hours of DVD viewing.
How I Test

Here at the About.com PC Hardware / Reviews site, I do not use the MobileMark application or the various tricks that the manufacturers may use to get their various numbers for advertising. Instead, I use a video playback test on all laptops and using the default power profiles and software settings that a laptop ships with. For laptops with a DVD compatible drive,Dell xps m140 battery this entails playing back a standard DVD movie in a loop until the system shuts down. On laptops without a DVD drive, in entails playing back a Quicktime based video loop until the system shuts down. This in my opinion gives some of the best real world usage numbers available.

In general, these tasks are some of the toughest when it comes to power consumption. Typically, such a test will result in anywhere from 50 to 75% of the manufacturers claim of battery life. Of course, this is just one method of testing. Dell xps m1530 battery People use their laptops in various ways and will generally get more battery life than this type of test but still below the manufacturer numbers.
What Consumers Should Do With Battery Life Numbers

Any consumer who is presented by a battery life number from any company or sales person needs to take this number and modify it to get a better idea of just how much battery life they would get. To determine this, you should really consider whether you use your computer heavily or lightly. A heavy user is someone that runs applications such as video editing, PC gaming or a large number of simultaneous applications. Hp dv6500 battery Light users are ones that typically only have one or two applications open at a time, use it primarily to browse the web or use productivity software.

Once you have determined the type of user you are, it is best to half the number if you are heavy users and subtract about one quarter if you are light user. For example, a four hour battery life claim will net roughly two hours of use for a heavy uses and about three hours from a light user. This is just an estimate because it is very difficult to determine how long a battery will run on a laptop until it is used in your typical fashion.