We would advise to use the parent unit on mains power wherever possible and only to use battery power for moving to another position where the mains power can be re-connected. However there are ways in which you can extend the battery usage. Adjusting the brightness to a lower level, and using lower volume levels will help to extend the battery life. Also in battery mode if you use the shortest (5 minute) power saving mode setting then the display will turn off after 5 minutes but the audio will still carry on working, and then when you want to re-activate the video just press any button.