Blinky
The Blinky is a probe that is inserted into one cell of a battery. It has a flashing Green LED that informs
battery maintenance personnel when the battery needs water, and when it does not as follows:
When the LED is blinking the battery's electrolyte level is OK and no water is needed.
In other words leave the battery alone!
When the LED stops blinking, the battery needs water so top up the battery!
The "Leave Alone" feature makes the Blinky suprisingly efficient. For example, if you have one hundred batteries equipped with Blinkys, and 50 are flashing while 50 are not, you just ignore those that are flashing and fill the ones that are not.
How simple, how efficient!