An auto battery does emit hydrogen gas when it is being charged or discharged but it does not contain gas per se.
It's extremely explosive and is also dangerous to breath. The sulfuric acid in the battery will be trapped in the fumes as droplets. This is very hazardous to your health. It is also known as Hydrogen Sulfate.
Sulfation can happen when battery is not fully charged and remains discharged
Answer 1 - Out-gassing of Auto BatteriesNO, the out-gassing from auto batteries while being charged, AND while being DISCHARGED is HYDROGEN [H2] which is HIGHLY FLAMMABLE, AND when mixed in the proper proportion [ratio] with air that Hydrogen gas is EXPLOSIVE.
It is always good to charge a battery to its full capacity before it is fully charged.
Usually from being discharged in below freezing weather. The water will freeze in a dead battery, expand, & swell the battery. This won't occur with a fully charged battery.
A battery float charger is intended only to keep a fully charged battery from losing its charge. It will NOT work to charge a battery that is discharged or damaged. Check the voltage of the battery to be charged. Do not use charger if the battery voltage is less than 9.6 volts.
Hydrogen
The acid turns to water. Batteries will freeze in cold weather if they are discharged. When the battery is charged, the water turns back to acid.
Yes, it shouldn't be any different from leaving your cellphone with a discharged battery in it. If you have an immobilizer or alarm, it may require resetting once the battery has been charged.
Recharge: By having a positive charge applied to the positive contact of the battery, and by having a negative charge applied to the negative contact of the battery. Discharge: complete a circuit between both contacts of the battery.
Hydrogen