2009 Macbook Pro: Service Battery, Replacement
If you have a 2009 Macbook Pro like I do, by now you have either replaced your battery or you need to. In my case, my battery wouldn't last even an hour on a full charge, and I had a "Service Battery" message in my toolbar. Fortunately, it is a simple, relatively inexpensive process you can do yourself in five to ten minutes, and afterward you should not have to do it again for another 5 years or so at least.
No need for a new tutorial; here's a great one from ifixit.com.
The only point I'd like to add is I don't believe you don't need to buy a $99 battery from ifixit or from Apple; Amazon has plenty of third party options available. I don't remember the brand I bought, but I did some research and checked reviews before purchasing. I didn't spend over $50.
You will need a tri-wing screwdriver, which is annoying since you probably won't use it for anything else. The battery I bought provided that and the philips screwdriver, included with the battery.