Quoting keto

*if* that is, as it appears to me, a car battery (or a pair of them), I sincerely hope you have the area well ventilated. They can and do give off hydrogen gas, which, if allowed to accumulate, is highly explosive. Let me reword that, it's explosive in any quantity but DANGEROUS if allowed to accumulate. Oh, the humanity, etc.

I admit I scanned the article rather than giving it a detailed reading, so if this is covered in there I apologize for redundancy.