Saving battery life

Saving precious laptop battery life?

Here's how to extend laptop battery life time with a few simple measures. The info here is based on nearly 4 years of continuous traveling with a laptop in the Middle-East and Asia.

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Laptop power saving

Roughly a laptop has 3 main components draining the laptop battery:

  • CPU - The center of the laptop coordinating all activity
  • GPU - The Graphics Processing Unit -
  • Screen - Where screen light comes from a CCFL tube or LED lights.

Effective laptop power saving means reducing CPU cycles (ie: Virus scanning, Computer Startup / Shutdown), less Graphics activity (ie: Games, Fancy animations) and lower Screen intensity. Additionally, power can be saved by turning off network cards (LAN, Bluetooth, Wifi).

Laptop battery life time and run time

A laptop battery has 2 main parameters:
53 WH Laptop battery with indicators - DELL C1295 

  1. Laptop battery life time - ie : 1 - 2 years from new to run down.
  2. Laptop battery run time - ie : 3 - 6 hours from full to empty.

Degraded laptop battery run time is an indicator for less laptop battery life time.

Saving laptop battery life time or extending battery life is done by reducing the amount of charge / discharge cycles. A simple measure to extend battery life is to run the laptop from the AC adapter only, leaving the battery out or replacing it with an old laptop battery in as placeholder. Next to this (ambient) heat has a significant deteriorating effect on how long a laptop battery lasts.

Thus by effective laptop power saving, reducing laptop power consumption, laptop battery life time can also be extended. Less power draw from a laptop battery results in less discharge - charge cycles.

Laptop power consumption

In a simple experiment a DELL Latitude D610 with a 53Wh battery is put on the test bench using a Watt meter. The measured values reflect how much power is drawn from a battery. For example putting the screen on low intensity saves 7 Watt for a CCFL powered screen. For LED screens the power draw is likely to be less.

 Laptop Power Consumption for a DELL Latitude D610
 Activity  Screen  CPU GPU  Battery  Consumption  Difference
 Idle+ON  Off Idle  Idle Full  18 W  -
 Idle+Screen  On  Idle  Idle  Full  25 W  7 W
 Idle+Battery  On  Idle  Idle  Charging  45 W  20 W
 Browsing + Battery  On Browsing  Browsing  Charging  60W  15 W
 Photoshop  On Maximum  Maximum  Charging  85 W  25 W
 Powered off  Off Off Off  Charging  20 - 30 Watt

Power is measured including power consumption of the AC power adapter. The 18 Watts measured when Idle in reality is lower when running on laptop battery.

Laptop power saving by disk defragmentation

The hard disk drive only has a marginal effect on power consumption. Turning the disk off when there's low activity makes very little difference.

However disk activity can prolong CPU cycles when fragmented. Running a defragmented disk saves CPU time.

Less known is defragmenting the system paging file, which comes into effect when RAM memory size is insufficient to run applications.

Laptops with little memory can benefit from a defragmented paging file. Defragmenting the paging file is done during boot time and can best be done after regular disk defagmentation.

Also defragmenting the hibernation file can easily save CPU cycles during wake-up or going to hibernation mode. Best is to disable hibernation mode before normal disk fragmentation and turning it back on when ready. 

DELL Latitude D610 power consumption

So what does an average laptop draw? The DELL Latitude D610 consumes about 30 Watts during normal usage without a battery in the bay. Installing an empty battery increases power usage up to 90 Watts.

The DELL laptop battery above has a capacity of 53WH - meaning it can output 53Watts during 1 Hour. With an average consumption of 25 - 30 Watts, a used laptop battery lasts for 1 hour and 45 minutes when the laptop is used moderately. In most cases it will last longer - when the battery is in good condition - because the frequency of the CPU is stepped down during low activity.