Thank you for your replies.
I think it would be interesting to put an induction ammeter over the battery anode lead with the generator switch both on and off and see if there is any drain. I'll see if our engineers can do a test.
I have heard of leaving the gen switch on after shut down before, so it is probably a good idea, even though not promulgated by EC. Something to do with the field windings being hard wired to the battery perhaps?
We have a GPU, very swish and locally made which we use a lot from home base.