Engine battery discharge issue

Hi All,
I pickup my 2009 AS Gloucester in two weeks and have a bit of concern over the engine battery life.
It has drained to zilch in a week when sat on the sold compound of the sales yard. 

The salesman has suggested that it is normal and he would arrange for a jumpstart when I came to collect it.

It will be having an engine and habitation service plus MOT before I collect it.

When asked about battery life in storage he suggested disconnecting the engine battery.
This seems like bs to me and I would like to hear any similar stories from AS owners and any suggestions?

You need to repost this in the coachbbuilt section or technical as not everyone reads the intro section.

Thanks Paul. The dealers have fully charged all of the batteries and monitoring the discharge over the weekend. There was an ambient drain of 0.3amps with the services turned off so checking security etc. I’ll let you know how it goes. 
Dave