Laptop Safety - Battery Life
How can I get the most out of my battery?
Getting more hours on a charge
For greatest length of battery charge, disconnect all possible external hardware, turn off the airport if you are not using it, dim the screen light as appropriate to your needs, shut down bluetooth, etc. These steps should help you get the longest use from a charge.
For more information, you can check out Apple's site: http://www.apple.com/batteries/notebooks.html
Getting the longest life from your battery
Like all lithium-ion batteries, our Mac computer batteries last a long time, can be recharged before completely discharging, and probably will eventually need replacement. To stave off the need for replacement as long as possible, it is good to use the computer connected to power to reduce the number of charge cycles. The MacBook batteries have an estimated life of 300 charge cycles. That doesn't mean each time it is charged, but each time it is charged 100%. So if it is used and charged 50% twice, that would be one cycle.
However, Apple also says that it is not good to use the computers connected to power ALL the time. The batteries do need to be used some to keep the ions flowing.
Also, if you are not going to be using the computer for an extended period of time, the battery should be discharged to about 50% and removed from the computer. Dead batteries tend to become unchargeable and fully charged batteries tend to lose the full capacity.