I'm monitoring my MBP right now. I'm at 4%, the battery indicator is now red, but no pop-up notification has opened yet (like a Notification Alert, or Badge or Banner like you would see on an iOS device).
Turning off the battery icon to see if any alerts or badges come up doesn't work either.
It seems there are no default low battery notification alerts in ML, that seems odd. Can anyone else confirm this? I tried Googling the topic but am coming up empty.