What is a battery status indicator?

A battery status indicator, also known as an "electric eye" or "magic eye," is a device used to display the status of a battery.  It is typically installed on Flooded Lead Acid Batteries and is designed to provide information about the state of the battery's electrolyte. It informs the user about the current condition of the battery, indicating when it needs to be charged or replaced, thus avoiding accidents or disruptions to the normal operation of devices due to insufficient power.