Many factors affect the amount of time that a portable computer battery can deliver power before it must be recharged. These factors include the configuration (processor, memory, etc.), types of applications being run and display brightness.
Dell uses industry standard benchmarks for battery run time claims. For more information on battery run times and benchmarks, the white paper, "Understanding Battery Life in Portable Computers" is available at: http://dell.to/2k0bUbu
Does an external keyboard produce the same effect? If so, Please try these troubleshooting steps. - Go to Control Panel and click on Keyboard. - Adjust the Repeat Delay close to Short and Repeat Rate 5 clicks less from Fast. - Click on Apply and OK then test it again.