Update...
I was fiddling around, and apparently "Notifications" is split across two areas in the app.
If you hit the "gear" settings icon, you get a page showing "Notification" as a menu item. Tap that menu item, and all you'll see is an option for "time lapse".
However, if you hit the actual device name, it will show a page with the "Notifications" Public, Rain, and Battery.
It's confusing as heck. Why wouldn't you group all the notification options together?
In any case, the "Battery" notification has never worked for me. It would also be nice if they had an "offline" notification.