I am no expert, but my hubby puts his Morgan on a smart charger (trickle charge) when it’s going to be sitting in the garage for any more than one week. I think he got this out of a book that a mechanic had written. The mechanic said the battery is constantly being drained by the immobiliser. So in your case... if the fan was left on and blowing that’s not good either. If I was you I would start with simplest solution and charge your battery.
Good luck
