Trials of a New Caravan

I bought a new caravan and started on the 'teething trouble' stage, but what happened really suprised me. After 2 days of the new caravan being connected to all utilities including mains electric my 'better half' told me that there was a beeping noise. This turned out to be the CO2 alarm. so it was removed from the caravan taken outside and after a while stopped beeping. The same thing happened the following day, but this time accompanied by a serious odour in the caravan. The answer was gas, but the gas bottle was turned off - amazingly the gas was  coming from the battery which had been ' fried' by the charger in the new caravan. By 'fried' I mean too hot to comfortably handle, bubbling with gas from each cell and took several hours to cool down when removed from the caravan. Strange as the same battery had been permanently connected to the charger in the previous caravan without fault. Has anyone any ideas as to what may have happened. Spare battery now fitted but not left on permanent charge. There is a serious issue here - the battery box is supposed to be sealed from the caravan to prevent gas ingress, but then as the battery box door is almost totally sealed where does the gas go ??  The caravan wasn't occupied whilst the above happened - very fortunate !!!!