Originally Posted by Jack L
If your charging system is overcharging the battery
will "boil" or bubble and produce hydrogen gas. This gas is HIGHLY EXPLOSIVE ! It's the same stuff hydrogen bombs were made of. The smell is usually described as "rotten egg" smell.
If this is in fact your problem, disconnect the power source as a spark could cause an explosion. Let everything cool down and ventilate the area. Next step, check voltage with a meter after things are cool. If your voltage is high you have a situation where your charger is overcharging and your battery
may be ruined also.
Be carefull ! When a battery explodes it is every bit as loud as a gunshot and acid goes all over.
Again do not do any testing until you are sure any build up of hydrogen is eliminated.
H2 does not have a smell I made the stuff most of my work life.
As part of battery maintenance check to make sure the vent is clear.
H2 is lighter than air and dissipates quickly.
It is unstable and reacts to light
as well as air hence the reason battery casings are not clear in color.
The H2 in batteries is generated from the H2SO4.