I've bought a Globemaster 'Off-road' camping-trailer that came fitted from new, with twin 105ah leisure-batteries, with the main (charging) 25mm2 cables wired-in to a 75a 'Anderson' connector at the tow-hitch, (nothing to do with 'normal' trailer-lighting!) I have got installed on the 110", a...

If all else fails, The earlier Mini ones fit!! You'll need to use your existing gear though

I had a similar problem a while back, when my 300 tdi 'appeared' to be siezed, it turned out to be that the Alternator had siezed, and was stoppimg the whole thing from turning over! Might be worth looking at it?