How to fix dashboard illumination problem 2004 Renault Espace 2.0l petrol?

I have a couple of issues with my recently purchased Renault Espace Dashboard. Firstly the display goes blank randomly and requires a tap ontop to get it back on but while it is out I lose all headlights, indicators etc. Secondly when I havemy headlights, heater, radio on in the car the illumination fades rapidly until I can barely make out any of the display. I don't know whether this could be down to a dodgy battery as it was left to run dry a few days ago.