macbook pro bulging case

Hi

I'm new to the forum but I have a very strange issue with my 2011 MacBook Pro... It has been unused for approx. 3 weeks, we have just come to use it and noticed the case no longer closes fully. Opening the case up reveals a deformed trackpad, lifted out of its housing completely at one side - this is what is causing the lid not to close. Also, there is a considerable bulge in the case underneath the laptop, so much so that it doesn't sit on its feet any more... Amazingly the machine still works - I am posting this question on it now! Has anyone come across this before? What has caused it? My first thought is the battery, the dropdown menu on the battery icon shows the message - Service Battery...

I don't have AppleCare and I daren't open it up to look inside since the lower casing is so deformed, pics attached. Specs as follows:

MacBook Pro 15-inch, early 2011

Processor: 2.2GHz Intel Core i7

Memory: 8GB 1333 MHz DDR3

Graphics: Intel HD Graphics 3000 512 MB

Software: OSX 10.9.4 (13E28)

Any advice gratefully received.

Thanks.

Keith