We would not recommend leaving your display on 24/7 if you are strictly running on batteries, as it will reduce your battery life. However, we do offer the feature on some of our newer released products. To see if you are able to do so, please follow the following instructions:
Remove the device from the wall plate
PREFS will appear. Center touch on this. You will then see either C or F, depending on your temperature.
Press on the left arrow once to arrive to Fade.
Center touch to get into FADE. Scroll to no, and center touch to save.
Place the faceplate back on the Zen and you will be all set to go.
Please let us know if you need any additional support. However, at this time, we cannot upgrade your unit to accommodate your request for this feature.