Hydrometers
The standard hydrometer for service men is known as the Type V-2B.
A special type hydrometer showing three colored bands in place of numbers has been designed for users.
The bands are red, green and black. When the hydrometer test shows the bottom of the red band in the electrolyte, the battery, whether in glass or rubber jar, is discharged. When the top of the green band is out of the electrolyte, the glass jar battery is charged. The top of the black band out of the electrolyte indicates the rubber jar battery is charged.