Does my car battery emit Hydrogen Sulfide gas when charging, or just Hydrogen gas?

I bought the battery around July 2014 (brand new), and because I did not drive my car for a period of one and a half months, it went completely flat. I tried charging it with my 3 stage charger, which did not seem to work - there was a constant rapid flicker of the charge light, I had the battery out of the car on a rubber mat, and charged for minimum 12 hours with no result. I then did the intelligent thing and connected my battery to my dad's old fixed-volt charger, which did the job.

However, because I do not use my car regularly, the charge in the battery has dropped low again. When looking at the battery now, it has dry residues around the terminals and on top of the case. Just wondering if the battery fluid might have been boiled by my dad's fixed-volt charger, and whether it's safe to use my 3 stage charger on the battery. My concern is that the battery might release Hydrogen Sulfide. I know batteries release Hydrogen gas as a normal part of the charging process, but do they release Hydrogen Sulfide gas, ever?

Note: the structure of the battery casing is completely sound with no signs of obvious damage from charging (unless you count the dry residue around the terminals), and I have always kept the cells topped with distiller water. And yes, I charge my car batteries in a well ventilated area so Hydrogen gas build-up is not an issue. It's he corrosive Hydrogen Sulfide gas that concerns me.

2 Answers 2


Yes it can produce Hydrogen-Sulfide, but usually only if overcharged (which may be your case). There is a write-up at the Battery University Website which talks about it:

Over-charging a lead acid battery can produce hydrogen-sulfide. The gas is colorless, very poisonous, flammable and has the odor of rotten eggs. Hydrogen sulfate also occurs naturally during the breakdown of organic matter in swamps and sewers; it is also present in volcanic gases, natural gas, and some well waters. Being heavier than air, the gas accumulates at the bottom of poorly ventilated spaces. Although noticeable at first, the sense of smell deadens with time and potential victims may be unaware of its presence.

  • 1
    It's worth noting that H2S is lethal in even small concentrations. If you can smell it you should leave the area immediately. Higher concentrations will deaden your sense of smell, meaning it can kill you without you realizing its presence.
    – Zaid
    Commented Jun 4, 2015 at 18:08

Check the water level if it has caps that can be pried off and add only distilled water if it needs topping up. Unhook the battery when not in use as the computer etc. is likely killing it. You can keep a good new style trickle charger/maintainer hooked up 100% of the time also. The hotter the temp where the battery is the faster the rate they discharge also! Car/truck batteries in fact store the best at very cold temps if fully charged first, like in a deep freeze.

  • Welcome to Motor Vehicle Maintenance & Repair! Something to realize when a battery is cold, while it may maintain better, using it when cold is another issue. Batteries will lose about 50% of their cranking ability at 0°F (IIRC). That will put a whammy on anything you are trying to start and is one of the contributors to hard starting in the cold! Commented Feb 28, 2019 at 19:40

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