Battery Water Level Indicator


Instantly know if your battery needs water!

Just imagine knowing the exact water level in your battery without removing the vent cap and without getting acid on your hands! No more struggling to peer into the vent hole to know whether your battery needs water or not!

Just remove the original battery cap and replace it with our level indicator. This product is so unique that it was recently granted U.S. Patent No. 10,361,468 by the U.S. Patent and Trade Office.

Battery Water Level Indicator Benefits:

  • Eliminates the need to remove the vent cap to check the water level
  • Saves time and effort
  • 360° sight glass allows viewing the battery water level from any angle
  • Water Miser™ technology reduces water loss
  • Dual spark arrestors
  • No electronic sensor to fail
  • No valves to malfunction
  • The acid-proof seal is included
  • Made in the USA

Quantity Discounts

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This battery water level indicator is available in several models. To choose the correct one for your battery, please read the instructions.

To buy, select a model number in the drop-down box below. Then enter the quantity and select the Add to cart button. Then select the Checkout button that appears at the top left.

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Testimonial- “They are perfect so far, our guys sure do like them!” – Don (Maintenance Supervisor – Texas USA)
Our battery water level indicators made their job of checking the electrolyte levels in their batteries much easier. They liked them so much that they recently ordered more. They installed the water level indicators on backup battery arrays in their oil refinery to ensure that correct water levels are always maintained.

Battery Water Level Indicator Installation Example

The picture below shows our battery water level indicators that were installed at the Texas oil refinery mentioned above. This set of batteries provides backup power to critical pumps that feed oil to their 40 MW generators. If one of these generators has a power loss, shaft damage can occur because of a lack of oil during the time it takes for the generator to coast to a stop. These batteries will give the oil pumps additional time to keep the generators supplied with oil until primary power has been restored.

Prior to using the battery water level indicators, it was a time-consuming task to find out whether the battery water levels were good or not. After installing them, the water levels of each battery could be instantly seen because the red mark in the sight glass can be viewed from any angle. Not only did this save their workers much time and effort, but it also ensured that each battery has enough water to prevent battery failure.

Battery Water Level Indicator installed in battery array

Features & Benefits

  • Easy to use and see.

A mechanical float with a red tip is easy to see in the sight glass. Knowing when to add water to your batteries is vital. If the battery plates do not stay covered with fluid, this can result in a ruined battery.

  • Patented Technology

The added Water Miser™ technology will reduce water loss in the battery cell. This saves you time and work since filling your batteries will be needed less often.

  • Easy Installation

The bayonet 1/4 turn installation will ensure a correct fit into the battery cell opening.

  • Safety

The flame arrestors will prevent any external spark from entering the cell. Since lead-acid batteries produce hydrogen gas, this feature helps to stop the ignition of this gas that forms in the battery.

A big problem with batteries is not knowing when to fill them with water. Without a visual reading of the water level, workers often need to devise watering schedules or carry out periodic inspections to maintain the batteries. With our Battery Water Level Indicator, the guesswork of knowing when to add water is gone. No schedules are needed, and less time is wasted. The red and green indicator ensures that mistakes are not made by workers so that your batteries are always properly watered to the correct level.

Several models are currently in stock to match the water level specs for different batteries. The chart below is for reference only and should not be relied on to know which water level indicator will fit on your battery. Please measure your battery before you order by following the steps below.

Battery Water Level Indicator Chart

Battery Water Level Indicator Chart

* The filling depth refers to the distance from the top of the battery to the top of the electrolyte when the battery is filled to the MAX level.
* The R Depth is the battery reserve depth of the liquid above the battery plates.

To view the M27X3-SIA threaded adapter dimensions, please refer to the part drawing.

Please measure your battery before you order by following the steps below. Use a non-conductive measuring tool and follow all safety precautions listed by the battery manufacturer.

1)  Check the vent cap mounting type of your battery. The most common types are 1/4-turn bayonet, threaded, and push-in. The mounting type of our level indicators is a 1/4-turn bayonet, and they will only fit on batteries of this type. However, we make an adapter that will fit M27x3 threads. No other adapters are currently available. To view the 1/4-turn bayonet dimensions of our level indicators, just click on the drawing links below. Then compare them to the dimensions of the vent hole on your battery to see if it will fit.

2) Make sure that the battery is fully charged. Failure to do so will affect the water level in the battery.

3) Make sure that the water level in the battery is full per the manufacturer’s specs. For most lead-acid batteries, the water fill level is 1/4″ below the bottom edge of the vent well.

4) Measure the distance from the top of the battery down to the top of the fluid. Then find the model number in the chart above that corresponds to the water fill level dimension of your battery.

5) This step checks whether the indicator float will hit the battery plates and stop functioning. This can happen if the battery was designed with a shallow reserve depth. Measure the distance between the top of the electrolyte and the top of the battery plates. That distance is called the reserve depth. Compare that dimension with the “R Depth” listed in the chart above for your selected model. If the dimension is less than the R Depth, cover the existing MIN line on the sight glass and put a new MIN line above the old line by the difference between the two dimensions. This will ensure an accurate reading.

To view the battery water level indicator dimensions, please select a model below.
#4000303 Battery Water Level Indicator

#4000425 Battery Water Level Indicator

#4000550 Battery Water Level Indicator

#4000600 Battery Water Level Indicator

#4000600 (with M27X3-SIA threaded adapter) Battery Water Level Indicator

Electronic water level monitors are prone to fail due to battery acid and harsh environments. Our water level indicator has a mechanical float made of plastic that is not harmed by battery acid.

Valves in single-point watering systems can fail. You simply cannot rely on them when the life of your batteries is at stake.

Fast, accurate visual inspection of a mechanical water level indicator is the only foolproof way to know when you need to add water to your battery.

How it works:

As the water in the battery slowly evaporates, the float lowers the indicator mark in the sight glass. If the mark is within the green area (see Fig. 1), you do not need to add water to the battery. When you refill a battery by adding water, the float raises the red mark to the “MAX” line (see Fig. 1). This indicates the battery water level is full, and no more water should be added.

When the mark is in the yellow area (see Fig. 1), this indicates that you should add water soon. If the mark is in the red area, you need to add water right away since low water levels can harm the battery.

If the red mark falls below the “MIN” line (see Fig. 1), in time the plates in the battery can dry out and ruin it.

Note- model #4000303 has one red O-ring instead of a MAX and MIN line. The red O-ring serves as the MIN line, and the placement height of the O-ring can vary depending on the specific battery model. If the indicator is above this O-ring, no water needs to be added to the battery.

When you fill the battery, use only distilled water, and do not add sulfuric acid. A battery will only lose water since sulfuric acid does not evaporate.

Custom float lengths are available to match the water levels of most batteries. Please contact us for more info.

Made in the USA. Dealer inquiries are welcome. For more info, please view the Battery Water Level Indicator Brochure. We give bulk discounts for 100 or more. Please contact us for pricing.

The Wikipedia site has a page on lead-acid batteries that is well worth reading. It covers everything from the history of lead-acid batteries to how they are made.

Note- this product is patented. The patent number may be viewed on our patents information page.

Additional information

Weight .05 lbs
Dimensions 5.5 × 1.63 × 1.63 in
Model #

4000425 (1.39" Fill level), 4000550 (2.50" Fill level), 4000600 (3.10 Fill level), 4000303 (1.25" Fill level)

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