I had a Drs MacBook Air that was dying from 100% after about an hour. She only had the ability to charge in the morning and at a lunch time break. So this was really making the device almost unusable for her practice.
The process of replacing the battery could not be easier. I think the whole process took me less than 5 minutes total.
I purchased the Pro Tech Toolkit about a 1.5 years ago. Still today I consider this one of the best investments I have made. It has come in handy with almost every computer repair I have done.