So whilst the a/c was being attended to today at the workshop I decided to crawl under the pax side of the dash and look at my CTEK 250. Dunno why but I did. Luckily. I found that the screw fitting with the plastic grip on it that holds the wire to the CTEK must have gotten hot at some stage as the plastic bit on the screw had melted. The connection in question is the alternator +ive on the CTEK.
Now I am unsure when this might have happened. Two days ago I had removed the aux battery and zip tied the battery terminals securely. But had not disconnect anything from the CTEK. I'm not sure if this might have done anything though.
I've looks at the user manual and can't see anything as to why.

Any idea's?