I jumped my truck recently from my wife’s car’s battery. I’ve jumped cars maybe 20 times, and I’ve always neglected to ground one of the negatives. I always involve all four terminals in the procedure – and on top of that, I do it in the backwards order of what’s normally recommended (I connect the clamps to the terminals in this order: live negative, dead negative, live positive, dead positive).
Anyway. I got to wondering how I’ve gotten away with jumping cars this way with no ill effects, explosions, shorts, etc. I looked around for some old threads, and noticed some references to dead batteries sometimes giving off enough flammable hydrogen gas to cause an explosion in the presence of a spark.
So … the first question I have is: is there any way to tell whether or not a dead battery is giving off too much hydrogen to be “ground-lessly” jumped safely? Maybe a test strip of some kind waved in the air over a dead battery?
My second question is: have I just been ridiculously lucky over the years to have had nothing happen jumping cars this way? Or have the odds been on my side all along?
(I had noticed also that some mechanically-knowledgeable posters – most memorably UnaPersson – seemed to be of the opinion that doing a groundless jump was reasonably safe, if not perfectly so. Some others, like Rick, were of the opposite opinion.)