a battery will for a gass cloud over the battery and a spark will set it off . this usealey happend in the summer when it is hot and no breeze blowing . you alwayes hook the + to battery and then hook the -to the engi block . it will put offa little spark and when hooking to a battery it is right in the gass . if you have to hook directley to battery do so in a breeze or fan over the battery to blow away the gass cloud .