I get a lot of questions regarding issues I have had in the past regarding my Macbook Pro and the infamous swollen Macbook Pro battery issue. Apple won’t always warranty your battery for you, especially if your Macbook is out of warranty or older than a year. The issue is that batteries aren’t meant to last forever and depending on the battery usage and how well the battery is taken care of, they won’t replace it. There are some tricks you can use to keep your battery performance at a high level. In a nutshell, you want to charge the battery to 100%, then unplug your Macbook and let the battery run to 0% without having the Macbook plugged in. Then let it charge while in sleep mode until it is fully charged. Its pretty important to not use your Macbook Pro while its charging during this procedure.
If you are experiencing issues with your Macbook Pro battery though, I suggest you take your laptop and the battery in to your local Apple Store. Don’t bother calling Apple Support, they’ll most likely blow you off. You just want to make your Genius Bar appointment and plead your case. In my experience, I talked to the head Genius at my local Apple Store (in Natick, MA) and he took care of me. He also gave me a receipt because my new battery was under warranty for a year.
In the case that Apple won’t replace your battery, I suggest you take a look at these NewerTech NuPower batteries available at Other World Computing. They generally offer better performance and a longer life expectancy. Hope that helps!