In many of the older, wet-type (lead antimony) batteries, they are shipped with a liquid installed called sulfuric acid. This electrolyte is energized during the charging process to maintain the proper voltage in the battery.
Without the proper battery maintenance, such as filling only with distilled water, these wet-type batteries are very susceptible to failure. As the voltage in the battery falls due to low electrolyte levels, broken cells, old age, etc., the automatic charger attempts to charge the defective batteries at a very high rate. The result is hydrogen gas escapes from these batteries via a vent. No battery is truly maintenance-free or completely sealed. This hydrogen gas is very flammable and can easily result in major fires. So, when you smell the “rotten egg”, address the problem immediately or call a certified emergency lighting service company.
