The "0 hg" label on a battery typically refers to "0 inches of mercury" (Hg), which is a way of measuring pressure in a vacuum or sealed environment. In the context of a battery, this could be referring to the fact that the battery is either not pressurized or has been designed to operate in a low-pressure or standard atmospheric pressure environment.
However, "0 hg" is not a common marking on most consumer batteries, so it might be specific to certain specialized battery types (e.g., in scientific or medical applications) or could be part of a specific battery's environmental testing information. If you’re seeing this on a typical battery, it might be best to check the manufacturer’s manual or datasheet for further clarification.