I have a similar problem:
I own a mid 2014 15” MBP with the original battery (it now has about 1100 cycles, with 70% health, as displayed by Coconut Battery)
However the battery didn’t present any problem besides reduced battery life (I can get at most 3 hrs), which is not a big deal for me.
Since a couple of weeks ago, though, my mac started to have a strange behaviour when I turn it on and the battery is lower than 50%: it boots up, I enter the password and it loads correctly, but after 20 seconds it shuts off, displaying the “dead battery” sign. The best part is that as soon as I plug it in, the mac suddenly turns on and gets back to the point I had left it before shutdown (no request of password, no loading screens…) and I can unplug it and it will work normally, with no problem whatsoever.[br]
I can’t really understand whether this is a hardware or a software problem![br]
This is what I tried so far:
SMC reset
PRAM reset
Safe mode mode (the problem persists)
Repaired the disk in Disk Utility (Recovery mode)
Any suggestions to try and address the problem?
Is battery calibration even a thing on MacBooks?