Looks like I might be having a similar issue. I’ve just received and installed a new battery from iFixit and the MacBook is shutting down abruptly anywhere from 5-30 minutes after switching to battery power. I’ve tried resetting PRAM/SMC/removing, checking connections and remove/replace the battery several times. This typically results in orange magsafe light, battery is detected correctly and it’s charging. Then after some time the magsafe the light goes green, battery is no longer charging and cononut battery shows NaN on battery capacitor indicator. I reinstalled the old battery and everything works fine - of course I have the original problem of diminished capacity which is why I replaced it. If several people are having similar issues I wonder if it’s a bad batch of batteries?