In batteries,
Hg stands for
mercury. Mercury is a chemical element with the symbol Hg and atomic number 80. It was once used in certain types of batteries, like mercury button cells, due to its stable chemical properties and ability to provide consistent voltage. However, due to environmental and health concerns, mercury use in batteries has been largely phased out or restricted in many countries.
So, when you see
Hg in the context of batteries, it's likely referring to the presence of mercury, though modern batteries typically do not contain it anymore.