Many problems with old battery of my MacPro Unibody. Replace it with Apple Assistance was too expensive and politics too many "terroristic": "don't touch the battery!!!". With 90 USD dollars and iFixit … bye bye Apple Assistance!
No problem at all. Fifteen minutes and the new battery was ok. Your instruction was clear and complete.
Read all instruction and be sure that the code number of the battery you want order is right for your device. For Mac, be sure also to have Pentalobe PS screwdriver. Then, don't worry and go easy!