The first one is by far the easiest. Simply dim your screen. Lowering the brightness by 50% will dramatically increase battery life.
Next, if you’re not using the Internet, turn off your WiFi. WiFi is a huge drain on your battery. Even when you’re not using the Internet and even when you’re not connected to a WiFi network, your computer is powering the WiFi transceiver and using precious batter power. So, if you’re not actually doing something online, turn your WiFi off.
Along the same lines, if you have Bluetooth accessories that you are not using, like an external mouse or a headset, turn them off too. There’s no point in burning battery life with Bluetooth if you don’t really need to. To squeeze every ounce of battery power out of your laptop, don’t use any Bluetooth devices at all. And, certainly limit the number of Bluetooth data transfers you do while on battery.
Next, some computers will spin your hard drive even if the programs you are using don’t need to access it. Go into power management in control panel or the systems preferences for Mac users and let the computer put your hard drive to sleep if it is not being accessed. This is a huge battery saver.
Then, there’s the battery itself. If you find that you’re always working on battery power, make sure you purchase the most powerful extra (or new) battery for your computer. Don’t be surprised if the manufacturer does not make battery. Battery specialists routinely offer better, more powerful, replacement batteries than the ones that ship with your hardware. The specification you are looking for is “mAh” which is an abbreviation for milliamp hours. The higher the rating, the longer the cell can provide power. If you have a choice between an 1800mAh battery and a 2400mAh battery for your computer, choose the 2400mAh battery, even if it costs more than 25% more. It will be worth it. (Obviously, if you can buy a second battery and keep it charged, you will be much happier on your trip — unless the extra weight is a problem.)
If you must play a video from your computer, do it from the hard drive instead of playing a DVD. The hard drive uses less battery power. And, if you know you are going to be on a plane or a bus with no hope of plugging in, transfer your video to a jump drive (USB 2.0 drive, thumb drive, etc.) and play the video from the USB drive with the hard drive turned off. This will use the least amount of battery power. Planning your entertainment in advance is a good idea. Also, remember your iPod/mp3 player is for music, not your computer — not when you’re trying to save battery life.
One last thing, if you are going to spend a great deal of time on planes, get a universal power cable that is airline compatible and use seatguru.com to check to see which seats on the plan offer power. www.seatguru.com is an absolutely awesome!
Actually, I do have one more laptop battery saving tip … leave your computer off and enjoy the scenery, grab a well-deserved nap or … heaven forbid, read a book. These final three methods are guaranteed to extend your battery (and your actual) life the longest. 
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