What magsafe adapter to use with my 15 inch Macpro

I have had a mac pro for almost a year now with no problems except for one. I bought it second hand, and it came with an 85w magsafe adapter. I noticed it's larger then my friends magsafe adapter that he got with his brand new. Our computers have identical specs and we're made during the same period.

The problem is, is that my battery started out with a few hours lifespan when I got it, and then I noticed it would shut off when the battery wasn't completely drained. It's been getting progressively worst since I noticed this. My mac suddenly shuts off when it gets down to about the 80% level. I heard that this was caused by a non matching power adapter. Do I have a 17 inch macbook pro adapter? Or does mine match? I plan on replacing the battery soon and before I do so, I need to know if the adapter needs to be replaced as well.

Help would be appreciated greatly!

As models get newer, Apple release smaller transformers on the magsafe adapters. I also believe that the new MBP's have a lower voltage magsafe power adaptor than previous models so I wouldn't worry yourself there.

In terms of your battery - it sounds like it needs to be calibrated. Go to Apple.com and search for battery calibration and follow the steps relating to your MBP.