Chosen Solution
Just replaced the battery in the MacBook Pro 13” with a new one from iFixIt. The battery shows up at 78% and is charging, I’m watching the mAh increase. The LED on the charger shows orange, as in charging. If I disconnect the power supply the computer won’t run on the battery alone, it must be plugged in, even though it has a charge. Any ideas?
Sadly, I think the switching logic which control the power source from the battery to the logic board is not working. It’s going to take someone with deep circuit diagnosis and access to the needed schematics and replacement parts.
