Charging my leisure battery via mains hook up

I am hoping this is a stupid question with a brief answer but being new to caravanning I though it best to ask!

I have my bailey discovery 200 hooked up to the mains at home and am assuming this is charging my leisure battery at the same time?

should i have the mains switched on or off in the caravan in order to charge the battery, the owners manual does not seem to cover it?

Many thanks in advance.

d