Expanding Battery on Macbook

Hi I have a Macbook pro 17inch intel 2.16ghz and out of nowhere I noticed my macbook battery expanding out of its shell. I immediately took out the battery and it continued to expand. Am I in danger of it exploding? Also is this manufacturer defect being covered by apple? I have had the laptop for about a year and a half, but this is obviously the fault of apple. Will they replace my battery? This is rediculous that this should happen. My wife also has a Macbook pro laptop, which is a little over a year old and she is wondering if this might happen to her too.