Macbook Pro shuts down after sleeping unplugged

IGraceHu wrote:

I have a 16-inch 2019 Macbook Pro. Every time I leave it to sleep for a long period of time, like overnight, without it charging, upon waking it will show the user login screen for a few seconds, then shut down. I don't know why it is happening but it has been acting like this for a few months now

There's nothing wrong with the battery health, it's reported as normal in Settings. The macbook is never low on battery when it happens and is almost always fully charged.

It's getting really annoying because sometimes I have unfinished work from the night before that just gets closed off

Try resetting the System Management Controller Reset the SMC of your Mac - Apple Support

look at your settings, make changes...

Determine battery cycle count for Mac notebooks

Determine battery cycle count for Mac laptops - Apple Support

if no insight or resolve-

Get help with your Mac notebook battery

Learn how to optimize the life of the battery in your Mac notebook, fix battery issues, and get service.

https://support.apple.com/en-us/HT