slightest spark can set the gasses off o a charging or freshly charged battery, weve done it twice pmsl
the last time we was trying to test a starter so had it sat on the battery whilst it was charging withj couple bits wire to the starter
i know duurrrr lol
fook me did she go bang, my ears were ringing for hours
the acids rots the fook outa ya clothes etc too, i take it ya have removed the batery ad washed the car down?