I read the instructions from IFIXIT. Printed them, and set them on my desk. The new battery arrived, it also was placed on my desk.

I spent the week with my son, wife and granddaughter.

I came home, battery was drained. The tools came with the battery. I followed the directions as I remembered them. Reassembled and followed the battery calibration directions.

I had it recharged, it held the charge for 24 hours @ 100%.

It states moderate skill level needed, I would think it is less difficult, closer to easy. My background is an engineer, automated machinery, programmer, and debugger, happily retired, but the directions were/are great. No reason for anybody to pay another to do the job. It will build confidence and let all DIY folk to realize that repairs are easy.