A few 12V battery questions

  1. I’ve read that an over-charged condition will cause a battery to vent hydrogen, but i’ve also read that a dead one will. Which is correct? I learned to connect the negative clamp to a good piece of metal in the engine bay of the dead battery; the reason is to prevent an explosion, right?

    2. In the parking garage at work I let a stranger use my battery to jump his car, he was nice enough and offered me $ in return so I said fine. He had his own cables and I stood by in an idle state as he proceeded to clamp the positive cable onto the negative terminal of my battery.

    Before I could say anything, POW big spark which removed part of the negative terminal itself. Well needless to say I learned my lesson the hard way and if someone needs a jump I do it myself. The car seems to be fine but I can’t help but wonder if the service life of the battery was decreased appreciably?


There is little chance that your battery is damaged but if your ignition were on it could have caused damage to the electronics. In fact, with the key off the reverse polarity can do some damage and often toasts fusible links and some relays. The best way to jump someone off is to remove the battery and get it charged.

  1. Batteries can vent hydrogen at any time, even when dead. Batteries will vent hydrogen when overcharged and when too big of a load is applied.

Please tell us where you get your batteries so we can get one too.

A dead battery won’t hold a charge, so charging it will lead to the same over-charged condition as over-charging a good battery. In both cases, you are charging a battery past its current capacity, so you should expect hydrogen venting.

Which negative battery terminal was partially removed, his or yours?

If your car is driving fine, count your blessings. It could have been a lot worse. Get your battery and your charging system tested to remove any doubt. Some auto parts stores will do this testing for free.

2 questions 1. Ive been told if a battery is drain dead 3 times its basically junk. 2. Is the (old wives tale) true that if you set a battery on concrete or the ground ect it will drain the battery.

  1. Every deep discharge damages a car battery. I’m not sure if three is really the magic number where the battery is too damaged to use. I would think it depends on the battery.
  2. No, not true. Putting a battery in a hot humid area will increase its rate of self discharge. (Even in a cold dry area there will be some self discharge.)

The battery drain myth is not relevent to modern batteries, but is based on fact. I found a cool link that explains it.


Yeah…i have heard heat is harder on a battery than cold…

All lead-acid batteries produce hydrogen when charging. When overcharged so that the cells are really bubbling, a lot of hydrogen is produced. A dead battery outgasses very little hydrogen (except when being charged), as the electrolyte is depleted and is mostly water at that point.

Your battery is probably fine. Hopefully your electronics are as well. I hope the guy gave you $$ for being a moron.

Wal-Mart was the last place of patronage!

Just to clarify, it was my negative terminal that got partially fried by the imaginably hot spark, but it is still usable. I should put a picture on here. He did give me $15, I guess I should be happy because it’s not every day that you get PAID to learn a hard lesson.