Service Battery Warning
ifixit.com sells a battery replacement (and almost any other part for your laptop), you might want to check it out. Here's the link http://www.ifixit.com/MacBook-Parts/MacBook-Pro-13-Inch-Unibody-Mid-2009-Battery/IF163-003

The part is out of stock, so you might want to be notified when it is available, it's all in the link.