VENTILATION, VENTILATION, VENTILATION. He is playing with fire literally. Batteries need to be either outside or in a compartment Vented directly outside with the vent above the battery as the hydrogen gas rises. You also have issues with corrosion and the gases that can produce along with the effects of acid hitting floors an other things. If you ever get chance look at a fire truck. Some of the compartments are vented to store batteries and/or gas cans etc. This is actually mandated by OSHA and NFPA.