My battery started dying, I would get around 1 hour of life out of my Macbook.
Changing the battery takes around 5-10mins and requires very little knowledge.
First place the laptop screen down and locate a small philips head screw driver.
Remove the 10 screws, see locations in the image.
Once removed you will see this.
Remove the two screws holding the battery down.
Disconnect the cable from the main board and remove battery.
Insert the new battery and reverse these instructions.