Bailey pegasus electrical problem on battery

by Rita
(Rochdale)

I have a Bailey Pegasus 2010 when I bought it the interior lights and radio would work from the battery with out the mains being plugged in, but for some reason when we went to it this year it would only work if plugged in.

We have had it serviced last week and was told the battery was a good one, is there a switch some were as according to the manual it should switch automatic from battery to car to mains electric.