Extending Battery Life

In faith that the article on battery life last month gave you a detailed insight of the battery life and the benchmarks available, this month let's focus on the key steps that you can take to maximize battery life. As discussed earlier, the types of applications run on the system have a major impact on battery life, but other factors also have a considerable impact. 

Referring to the MobileMark 2002 results given in Graph 1, you will see that the two top power consumers are:

• Display power: Power consumed to create the image seen on the notebook screen
  
  Rest of system: Power consumed by the remaining non-specified electronic components in the system such as the core-logic chip set and memory. The processor is a
  distant third in the MobileMark 2002 results because typical business-productivity applications are not compute-intensive. The mobile processors used in most of today's notebooks usually consume only 5—8
  percent of the total system power when running mainstream business-productivity applications. 

The second top power consumer (rest of system) is a catch-all category for components such as the system memory and core-logic chip set that are too difficult to measure
independently or do not individually contribute significantly to power consumption. The top power consumer is
display power. 

Let us now discuss the impact of display brightness on the power consumed by the
system.

Display power consumption

The display subsystem creates the image seen on the portable computer screen. The single largest consumer of power in the display subsystem is the display lamp, which governs brightness. The brighter the lamp, the more power is consumed by the display system and the shorter the battery life. The figure that follows compares the expected battery life when the display is set to minimum and the brightness level is set to maximum. In Graph 2 (shown on next page), the MobileMark 2002 battery life ranges from 3 hrs and 23 mins associated with maximum display brightness, to 4 hrs and 50 mins at minimum brightness. These benchmark results suggest a battery-life increase of over an hour associated with adjusting the brightness of the display from its highest to lowest setting. As the brightness setting has such a powerful impact on battery life, most notebooks are configured to automatically dim the display as the AC power is removed and to increase the brightness when plugged back into an AC outlet. To save even more power, display brightness can be manually adjusted using the Fn keys on the keyboard of Dell Inspiron, Latitude, and Dell Precision mobile workstation systems.

Other power savers

Other steps that can be taken to extend battery life, include enabling Windows OS and device power management capabilities. n Enable MS Windows features
Windows' settings can have a significant impact on the battery life. As of now, Windows provides the ability to extend battery life by trading off power consumption and performance using 'Power Schemes'. You can access these from 'Power Options' icon in the Control Panel. For best battery life, select the 'Portable/Laptop' or 'Max Battery' power schemes, that turn off devices such as the display and hard drive during periods of inactivity, and adjust the processor power. The 'Portable/Laptop' option dynamically adjusts processor power and performance depending on the application running on the system. When performance demands are low, the processor is kept in a low power and performance state. When demands are higher, the processor runs at higher power and performance levels up to its maximum capacity. In contrast, the 'Max Battery' setting forces the processor to its minimum performance level until the battery power becomes low. At that point, the power scheme increasingly forces sleep periods on the processor, further limiting processor performance as the battery becomes more depleted. This can extend battery life but there is significant performance degradation. In contrast, none of these power-saving techniques are applied under the 'Always On' power scheme, which is designed for maximum performance, but results in the shortest battery life. Today Windows also allows users to disable certain hardware devices that are not used when the notebook is on battery. This is accomplished using the 'Windows Device Manager' accessible in the System icon of the Control Panel. For example, a system can be configured to temporarily disable the 10/100/1000 Ethernet LAN controller when running on battery. Or, executing the above process, while on battery, will automatically disable the device when the system is running on battery power.

Device power management

Some system devices, such as WLAN devices, have built-in power management capabilities. A WLAN device can consume significant power to maintain a minimum traffic between the notebook and nearby wireless access points at all times. You can enable the power management features built into many WLAN devices to allow the notebook's power-management software to reduce power consumption of the device. These features can be enabled in the wireless device software, installed on the notebook.

Additional steps

Further, a user can take additional to maximize battery life. One is, if feasible, mute audio when running on battery power as the audio power consumption can have a noticeable affect on battery life. In addition, install a second battery, rather than an optical drive, in the portable drive bay. This not only extends battery capacity, but also eliminates the significant power consumption associated with the optical drive. Programs run from a CD or DVD can be copied to and run from the hard drive, so as to consumes less power than an optical drive. Another easily overlooked way is ensuring that your system is equipped with adequate system memory. If a notebook doesn't have enough system memory to run the OS and applications, it will use the hard drive for working space in a process called 'paging.' This process increases activity on the hard drive.

Reading from and writing to the hard drive, rather than system memory, consumes much more power.

Therefore, as the first important step in maximizing battery life, you must choose a notebook that is equipped with a mobile processor designed with power management in mind. It is also important to enable the OS and device power management capabilities. Further you should disable devices that are not used when running on battery power, and replace the optical drive with a second battery. Finally, it is important to address the top power consumer in the system-the display. Lowering the display brightness when running on battery power is one of the most effective ways of extending battery life. For this reason, most notebooks are configured to automatically lower display brightness when on battery power. 

Brightness settings

Some notebook manufacturers limit the maximum brightness that can be set when on battery power. This practice improves battery life but greatly reduces the visibility of the screen under high ambient light conditions such as a brightly lit room or outdoors on a sunny day. This practice can also impact published battery life benchmark tests run by notebook manufacturers and industry magazine test facilities. For this reason, the latest MobileMark benchmark test recommends that the display on a tested system be set to a specific brightness level or 'luminance' measured in cd/m2 (candelas per square meter), also known as 'nits' in the US. The recommended level is 60 nits. Notebook LCDs generally range from about 20 nits for the dimmest setting to a maximum brightness of 150-180 nits on some of the brightest displays currently available.

Therefore, ensure that the notebook you buy has a battery tested in a facility that has equipment to measure the surface brightness or luminance of a display. This way the actual display brightness level of tested systems will not vary between the manufacturers, thus, giving unbiased battery life benchmark results. QuickSet is one such software interface available on Dell notebooks. It makes it easy to customize settings for travel or presentations, and its power management interface provides quick access to standard or customer-defined power schemes. Using the Power Management Wizard, a customer defines settings for standby and hibernate modes, as well as power schemes that can turn off the display and hard drive, set display brightness, and define wireless activity. These schemes are customized for
operation on and off battery.

Gary Verdun, Technology Strategist, Office of the Chief Technology Officer, Dell