How to Read the Indicator Eyes

Many people incorrectly interpret the status of an indicator eye to mean “I need to water my battery”. These notes explain how to “read” a set of indicator eyes on a battery.

Do not even look at the indicator eyes if the batteries are not fully charged.
The charging process changes the electrolyte level in a battery. The electrolyte level will be significantly higher in a charged battery versus a discharged battery. This is why you are always instructed to only water a fully charged battery. The indicator eyes on a discharged battery will be down even if the battery has exactly the correct amount of electrolyte.

Do not water based only on an indicator being down.
Watering should be done based on usage. In a typical fleet application, watering twice a month is sufficient and certainly no more than once per week. A residential user should not need to water more than once a month.




Look at all of the indicator eyes. You can tell something about the system from the state of the eyes before watering.

  • If all of the eyes are down except for one (or two) and this one has the indicator fully up, pull out the valve and check for interference with the float, free movement of the valve mechanism, and water in the cell.
  • If all of the eyes are up or mostly up, your battery may not need watering. Make sure you are not watering too frequently.
  • If all of the eyes are down or mostly down, this is what you would expect after a couple of weeks of use. 

The flow indicator should be turning. Watch the indicator eyes. They should pop up at various times during the watering cycle depending on how much water each cell needs. When they are all up, the flow indicator should stop. If all of the indicators pop up immediately after starting watering, you have a pressure issue. Make sure you have not removed the pressure regulator if you are using the watering gun or direct fill link. This must be resolved before your batteries will be correctly watered. If you need assistance, call BWT at 877-522-5431.


When the flow indicator stops, all of the indicator eyes should be up. It is not unusual for the indicator eyes to drop slightly after the delivery system has been disconnected. Water pressure tends to hold the float slightly higher than its natural buoyancy level. Seeing a slight drop also confirms that there are no interferences with the float’s operation.