Well, the machine is from 2016 and I thought that maybe the battery was starting to swell a little. Why did I think this? The track pad looked as if it was a little bent and the haptic feedback stopped working. These two symptoms led me to replace the battery.
Well, the kit and online instructions were 100% PERFECT! Two things were difficult: 1) the glue holding the battery segments in place!!! and 2) putting the small cable from the board to the battery connection. It was VERY difficult to know if the cable was fully inserted or not. Visual clues on the cable were severely lacking, to know if you had it right.
When I was finished, the computer booted without ANY problems. However, the haptic feedback is still non-functional. I've gone through every possible corrective measure that is built into the Apple OS, to no avail. The only thing remaining would be to replace the track pad. Since haptic feedback is just a "nice to have", I'll not spend the money on it.
BEFORE starting your own repair job, go through EVERY other logged experienced you see with the instructions. The base instructions are great, but you learn even more from others' experiences and you NEED to heed what they share with you. One thing I learned from the other comments was the warning about the small washers on the track pad. If you use a bit of common sense, this won't be a problem and all of the washers will stay where they belong. Also, one commenter wondered why you should even remove the track pad...if you do not, you will get glue solvent all over the track pad's underside and possibly damage it. Just follow the instructions and all will be well. :-)