Why does macbook turn off at 80% battery?

Question

macbook

Macbook Pro 13 2017, less than a hundred recharge cycles
Usually used on mains power and did a full recharge cycle a couple of times a month.
100% charge and when I try to turn it on it says that it is discharged
From time to time I look in coconutBattery and when powered from the network it always shows that the battery consumption is 0 watts, which means that everything is in order with the power supply and my battery really does not use 95% of the time I use the laptop and I don’t understand at all how it can fail in such conditions
Design Capacity in coconutBattery jumps when restarting the laptop, usually shows 50-80%, most often 67%
NVRAM and SMC reset, macOS reinstalled
Will replacing the battery help in this case or is it something else? Theoretically, after all, a battery with 100 cycles should be more alive than all living things.

Answer 1

To service. Maybe marriage, maybe something else. Telepaths are on vacation, and macbooks are not such a technique that you can climb into with a soldering iron and a multimeter

Answer 2

I would be in your place.
I would go the other way, for example, the keyboard misses the keys. I would apply for a service (and there is post-warranty service with keyboards), the keyboard changes with the battery. That's how you would solve your problem.
Well, either in the service to apply for battery diagnostics. At the same time, look at recall campaigns for your MacBook. It seems that if my memory serves me, there were some in the 17th year, with battery problems. I'm currently working on this (my wife's laptop, I'm waiting for silicones), at the beginning of the summer they changed the keyboard just.