Carver rapide Ge water heater

Hi, I'm really new to modern caravan towing and I have purchased a Elddis Typhon EX2000. I have read all the instruction books that have come with it and I am unsure about the heater. What do the pictures on the control unit mean.  a 'I' / Battery / flame / flame with line through it.? How do I know that the mains and gas are being used at the same time and do you leave it on all the time you are on site or only when you need hot water.  Gratiful for your comments.....