Battery life is an important aspect to any traveler who needs their laptop to last as long as possible. Sometimes you just need to get work done, but you don't have an available power source nearby. That's why I have compiled a list of things you can do to help squeeze every last minute of battery life from your computer. Some of the tips will help out a great deal, while others will only provide a small benefit (if they are bundled together, they may make a relevant difference). Either way, read on to extend your battery life to its limit.

1) Turn off Airport
As long as there are no 802.11b/g/a networks within range, or you don't require Internet access, turning off the built in Airport can help with battery life quite a bit. If you do need Internet access, and you can connect via ethernet cable, that would be much more energy efficient than using wireless.
2) Turn off Bluetooth
This option is likely more practical that turning off Airport, but it won't provide as much of a benefit. Most of your Bluetooth devices aren't needed while on the road, so it makes sense to turn that feature off, and just use the built-in input devices and wired connections when battery life is more important than being cool.
3) Avoid using the built-in iSight camera
The Apple MacBooks and MacBook Pros sport a built-in iSight video camera. While taking pictures with Photobooth, conducing video iChats, and making sure you hair is straight might be fun when you are connected to an outlet, they can be a real drain on battery life when you're not. Therefore, keep that camera off to save a little juice.
4) Keep discs out of the DVD drive
One of the few motorized parts in any laptop is the optical drive. The motor required to spin DVDs and CDs can use a lot of power. Thus, keep the drive usage to a minimum to keep battery life at a maximum. If you insist on watching DVDs, rip them to your hard drive before your trip with a utility such as MacTheRipper.
5) Turn down the screen brightness
Those cathode tubes lighting up your laptop's screen are one of the biggest power draws in the computer. Turn down the brightness of the screen to as low as you can comfortably work, and your battery will thank you.
6) Invert the screen colors
Keeping with the theme of reducing power consumption via adjusting the display, many users have reported extended their battery life by inverting the screen colors. This can be accomplished by navigating to System Preferences -> Universal Access and choosing the radio button next to "White on Black" (or alternatively use the keyboard shortcut Control+Option+Command+8). The theory is that every pixel (of which there are over 3 million on the 15 inch MacBook Pro) requires a small voltage to twist into a state that allows light to pass through. By inverting the screen, more of the screen in covered in dark pixels, which should take less voltage to twist.
7) Turn down/off the backlit keyboard
The other major light source in the MacBook Pros is the backlight in the keyboard. While you don't have to worry about this in a bright environment (because of the ambient light sensor), if you are working in a dimly lit area, then the backlight might just turn on. Like any light source, it requires energy. Turning it off will prevent it from using any power, and turning it down will make it use less power.
8) Turn down the volume level
Moving the little magnets back in forth in speakers can take a surprising amount of electricity. Although the speakers in laptops are small, they still require energy to operate. If you don't need iTunes blasting away, turn off the sound. If you do need to listen to the audio your computer is creating, plug in some headphones. They will likely require less juice than the built in speakers.
9) Run fewer applications at once
Mac OS X is an operating system built for multitasking. Because of that, it uses a paging scheme which will move unused parts of memory to the disk when other applications need that memory. The hard drive is another big draw on the battery, so avoiding any hard drive usage is a good idea. By running less applications simultaneously, or installing more RAM, you reduce your risks of having memory paged.
10) Turn off logging
The same logic from the last hint can be applied to log files. Some log files on your system can gather a lot of data, keeping the hard drive active, and running your battery down faster. If you can, turn off some of the logging abilities to reduce hard drive usage. One such log that generates a lot of entries, and is easy to turn off is the firewall log. Open System Preferences -> Sharing, click on the Firewall tab, and click the Advanced button. In the sheet that pulls down, make sure that "Enable Firewall Logging" is unchecked.
11) Turn off Spotlight indexing
Since the hard drive is such a heavy power user, it makes sense to have another method for reducing the usage. If you don't use spotlight often, or feel you can live without it while traveling, turn off the indexing to prevent it from keeping track of all hard drive changes. To do this, open System Preferences -> Spotlight, click on Privacy, and drag your hard drive to the indicated area.
12) Turn off background notifications
Various applications provide a method to notify you of a change, even if the application isn't active. To accomplish this feat, a background daemon must be running at all times. This daemon will use a small amount of memory and possibly the hard drive/CPU at times. By turning off these notifiers, you will deactivate the daemons, possibly saving a small amount of power. One example of a program that provides this functionality is iCal, which can display its calendar alarms even when iCal is not running.
13) Turn off some of the services in Directory Access
There is a program in your Utilities folder called Directory Access. It is used to enable/disable certain services including Bonjour, Samba, and AppleTalk. Some of these services will constantly be polling for active devices to connect to, which can incur another very small drain on your battery. I would recommend never turning off Appletalk, Bonjour, and SLP, but the rest are fair game. If you don't know what one of the acronyms stands for, Wikipedia probably knows.
14) Do NOT disable a CPU core
The MacBooks and MacBook Pros all feature CPUs with two cores instead of the much more common one. These two cores provide for a huge speed increase in all multi-threaded applications (nearly everything these days). Because there are two cores running, it is logical to think that turning off a core (using Apple's CHUD tools) will reduce the power requirement of the CPU (at a cost of processing power). Actually this is NOT the case. These chips were designed to run most efficiently with both cores active. Disabling one not only requires more power, but also generates more heat, a double whammy! Some users have reported losing up to 40 minutes of battery life by turning off a core!
15) Keep it cool
The fans in the MacBook and MacBook Pro are designed to turn on, or speed up, at certain thermal thresholds. If you are able to keep your laptop below those thresholds, you will keep the fans off, and conserve battery power. One way to keep it running cooler is to perform less CPU intensive tasks. That's not always an option, but using a laptop riser is. Something like the RoadTools Traveler CoolPad (I receive no compensation for that link, or for clicking on it) will keep your MacBook running cooler at all times.
16) Disable unneeded features
When was the last time you actually used the remote control for your MacBook? If you're anything like me, you have played with it a few times, but have only gotten good use out of it once or twice. Therefore, why are we wasting battery power on the IR receiver when it goes unused 99.5% of the time? To disable the infrared receiver, open up System Preferences, select Security, and check the box next to "Disable remote infrared receiver". This will result in the IR receiver being shut off, and also OS X will not be monitoring that port any longer. The result will be very small, but every bit helps.
17) Calibrate the battery once a month
Finally, if your battery is showing signs of shorter run times, you may want to calibrate the battery (Apple recommends once a month, but I would say once every three months would be fine, depending on your usage patterns). To calibrate the battery, follow these steps:
  1. Fully charge your MacBook/MacBook Pro.
  2. Once fully charged, leave it plugged in for at least another 2 hours.
  3. Remove the MagSafe power adapter, and use your computer until you get the battery level warning message.
  4. Ignore that message and keep working.
  5. Eventually the machine will go to sleep.
  6. Do NOT plug it in. Instead, let it sleep for at least 5 hours.
  7. After the time has passed, plug it back in, and let it fully charge.
  8. Once fully charged, your battery has been properly calibrated.
18) Turn off or reduce frequency of auto-saves
Many applications have the ability to auto-save your latest changes on a pre-set frequency. This is great for making sure you don't lose data, but terrible for battery performance. If your data isn't critical, consider either turning off or reducing the frequency of the auto-save feature. For example, TextEdit auto-saves every 30 seconds by default. If you are just taking notes using TextEdit, this is keeping your hard drive active much more than really needed, draining your battery life.
19) Use Safari or Firefox private mode browsing
Both Safari and Firefox have a feature called private browsing. This feature in intended to hide your browsing history, cookies, cache files, etc. when your browser session is ended. But you can also take advantage of this feature for battery life. When in private mode, the temp data is stored in memory rather than the hard drive, which is much more battery friendly.
20) Turn off auto-check for some or all email accounts
If you are like me, you have 8+ email accounts in Mail.app (or your favorite email application). However, many times a majority of those accounts don't receive many emails (many once per day). If you need to keep your email client open, consider turning off auto-check for those accounts to reduce network and hard disk usage.
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