MacBook turns on with Charger only but stays on if unplugged
So I have an Early 2015 13” MacBook Air.
I had to unplug the battery and plug in the charger to get it to boot. Prior to this, the MagSafe charger would show the Amber light and change to Green when pressing the power button before reverting back to Amber a few seconds after.
Now after I got it booted, I shut it down, plugged the battery back in and booted it back up with the charger plugged in. Now the system says the battery is 90%+ charged.
I unplug the charger and the system stays on. I try shutting it off and booting from the battery and it doesn’t work. The battery health status is normal and only 400 cycles.
Any ideas as to what is going on and how I can fix it?
Thanks in advance!
Update (01/04/2019)
Is this a good question?