2014 Ducato / Bessacarr battery isolation

I wonder if anyone is able to offer me some advice.  I am a year into the joys of motorhome ownership (family, 2 young kids, loving it) and am still on a fairly steep bit of the learning curve!  Insights from those of you more experienced on ths forum are
really helpful to me and I keep an eye on posts.  Please excuse me if this is a daft questions.  

After about 3-4 weeks the vehicle battery on my 2014 Ducato-based Bessacarr 496 is flat and needs jump stating.  Is this par for the course for those of your running similar vans?  It doesn't seem that long to me for a new battery which is, according to
its recent habitation check, in good condition as you would expect at 12 months old.  

Around the barrel where the ignition key inserts there's a red bit of plastic.  The rather sketchy users manual imples that this might be a way of isolating the vehicle battery.  Preumably it drains all the time for the remote locking, for example?  This
is where the question gets a bit daft.  I cannot work out what to do to the ignition barrel and that bit of red plastic to isolate the battery.  Has anyone else got a new Ducato with a similar isolator who can tell me how it works please?

Thoughts much appreciated, and apologies for my ignorance.