Catherder
Professionals work on facts established by examination and report. Speculating as to whether it was a propane leak or overheating battery on charge is anything but professional.
My only comment is confined to the evidence in photographs above together with the deck plan. A sleeping space for 30 or so people with only one entrance/exit via a galley is unsafe if a fire breaks out in the galley/escape route.
One only needs look at the Buncefield explosion where a petrol vapour leak combined with a totally still air night in mid winter combined to create the biggest peace time explosion in UK history to understand that if something can go wrong… it will.