Hi There, I have just bought my first caravan 2 weeks ago, when I picked it up the dealer explained what all the buttons and bells were but I have forgotten what he said about the small black electrical unit behind the battery box. It has printed on it....Input 240v...output 13.8v. Is this a voltage reducer to operate the 12v system, or is it a battery charger, or is it both, and, is it ok to use the electrics without a battery fitted or will this damage the system. The van is a 94 bailey