For anyone interested in this matter, I can save you time by reporting that the various forums on the internet have the full spectrum of answers to this question. At one extreme are folks warning that batteries of any chemistry (even gel) that do not have vent hoses MUST be placed in a well ventilated area. On the other extreme are calculations that it would take days of continuous overcharging to hit the lower explosive limit in an air tight 100 cf trunk, and reminders that trunks are not air tight. They are ventilated so that odors don’t accumulate. In the middle are confused people like me who have driven VWs and Miatas and BMWs for decades without ever thinking about this.
I don’t trust the LEL calculations because I have seen failed flooded batteries that gassed like crazy.
This forum often has someone who really knows their stuff on almost any topic.
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