Backup RAM, what does it save?

For a few weeks I thought the battery replacement in my MVS went bad (as it wasn't saving), because my games don't keep the High score (I've been using the same 4).

but now that I'm using a Universe Bios, I realize the Mode (MVS-AES) and region settings, stay in the same state I left it the last time.

So I'm confused on what the backup Ram actually preserves.