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.)
Actually measuring the amount of hydrogen released, or its concentration in the air immediately surrounding the battery, probably requires sophisticated equipment. Furthermore, I’d venture that it’s difficult if not impossible to get precise results, as any number of variables (temperature, air currents in the room, etc.) could have an effect. So I wouldn’t be surprised if no one has actually run a test to measure the released hydrogen. It’s also not really feasible to empirically test what percentage of the time an explosion will occur with a careless hook-up procedure (damn hard to get volunteers).
Probably the best gauge we have as to how dangerous it is lies in reported incidents of battery explosions. More than zero, to be sure, but if you compare how seldom we hear of this to how many batteries are jumped every day/month/year, it seems the odds are mighty low.
Of course, it’s like Russian Roulette, where the odds are only ~15% that you’ll get the bullet, but if you’re in that unlucky 15% you’re 100% dead. And if you don’t pull the trigger, you’re safe. Making the last jumper cable hook-up far enough away from the battery to prevent spark ignition of the hydrogen is the equivalent of not pulling the trigger.
I would say that if your last connection and first disconnection is at the donor battery rather than the one being charged, that in itself minimizes the chance of an explosion. Presumably said donor battery was already fully charged and emits little if any hydrogen.
It is going to be imposable to top Gary but my question although covered by Gary differently is;
knowing what the proper hookup procedure is and just doing it the opposite, Why?
I have been very close to several battery explosions, and they are very loud. The mechanic’s that were working on them got away with very minor burns and some clothing damaged. One had some hearing loss, as he was down in a pit if you will on a large hydraulic excavator. Large battery(s) also, one of 8 blew.
The others involved batteries in boxes (on trucks) and the liquid was very low and they all blew out to the side.
I am extremely cautious around batteries, as the last one that blew where i work, the Mechanic just moved the cable and being loose caused the spark, and was probably the reason for the partner battery to be run down.
Don’t mistake all the incidents i am relating to mean it can’t happen on you car.
