Pie 9.0 Low Battery Notification Not Working (Moto G7)
TLDR; You either get battery saver, or notifications; not both.

There seems to be an issue with the Android Pie release, or a subsequent patch. When the "Battery Saver" function is turned on, it automatically disables the "Low Battery Notification" features. Or, the battery saver fires and prevents the low battery notification from firing by default. "Save the battery" instead of making noise, popping up a message, and vibrating. I turned off the "Battery Saver/Turn on automatically" function and now my phone interrupts whatever I'm doing to let me know I need to plug in soon.