I have a MacBook Air, with Catalina 10.15.2. When I start it up unplugged, with a full battery, most of the time it starts up and then immediately shuts down. When I hit the power button again, it shows the red power indicator with 0%. I plug it in and it launches just fine.
I brought it into the local Best Buy and they ran hardware diagnostics and said everything looks fine.
How can I get it working without cord ?