Twice already, I've lost all my game progress without saving, because my battery ran out while I was playing in full screen.
Mac OS X normally gives a notification when you reach "reserve battery" power, which gives plenty of time to plug in or save.
But, when playing OpenEmu in full screen, I cannot see the usual "reserve battery" notification.
I think the best behavior would be is to exit full screen when the "reserve battery" happens, so that the user can see the notification. Alternatively, OpenEmu could monitor the battery, and give the user periodic notifications.