Instantly determine your batteries water level at a glance. The entire battery can be assessed in a fraction of the time it takes to manually check battery water levels.

No electronics, no connection to an outside power source, no sticking valves and no guesswork.

Keeping water in your battery is crucial to maintaining the health and longevity or your battery.

Now with Water Miser Technology built in to reduce watering and keep your battery clean.

  Level Indicator
Instant feedback on battery water levels
No more Dry or under-watered battery cells
Built in Spark Arrestor of added safety
Less Guesswork = Less Maintenance
Fast and easy to install using 1/4 turn industry standard bayonet vent attachment
Does not rely on electronics or batteries.
Batteries stay clean and use less water through incorporated Water Miser Technology

Dual measurement gages on front and back of vent cap. Maximum - Minimum & Precision Color Gauge


Currently available in two float lengths to achieve these fill heights: 1 3/8" (#4000425) and 2 1/2" (#4000550). Custom float sizes available for any size battery.

Fits all Rolls Surrette 4000, 4500 and 5000 series batteries.


 Quantity  Unit Price
1-18 $6.50
19-48 $5.25
49-100 $4.39
101 + CALL (419) 290-1103 FOR PRICING

  Battery Water Level Indicator
  1.39" Fill Height

  Tall Battery Water Level Indicator
  2.50" Fill Height

  CUSTOM SIZED FLOAT?   CALL US AT 1 (419) 290-1103  
  Volume, Wholesale and Distributor discounts available for qualifying orders  

- L16 Group Batteries - Use #4000425
- Rolls Surrette 4000 Series Batteries - Use #4000425
- Rolls Surrette 5000 Series Batteries - Use Tall #4000550

NOTE: Please measure first to assure proper float size.


You have two options for determining which Battery Water Level Indicator you need for your specific make and model of battery.

1) Measuring your batteries Water Reserve Capacity
Start by making sure you always have the proper safety equipment when working with any battery. In addition to gloves and goggles, you will need some type of device to measure the level of water inside the battery. Wood items like a chop stick, wooden Popsicle stick or food testers work best.

Correct Water Level Measurement

Remove the existing vent caps from your battery. Check to make sure the internal plates are covered by at least 1/4" of water, then charge your battery. Never fill your battery all the way with water prior to charging in order to avoid an overflow of electrolyte (Water + Acid). Electrolyte in your battery will expand once the battery begins to generate heat during charging. If the battery is already at capacity, water will be forced to escape through the vent which can cause a potentially dangerous situation due to the caustic nature of the sulphuric acid. So remember, put water into your battery after the charge cycle.

Once the batteries have been sufficiently charged, add enough water to bring the level up to approximately 1/4" below the vent well. The vent well is the tube that you look through to determine your batteries water level. Once your battery is at the correct level, insert your measuring device down into the cell being careful to only touch the tip of the measuring device to the very top of the water.

Next, hold the measuring device against the side wall of the vent well. Take a pen or pencil and mark the measuring device right at the spot where it reaches the top of the vent well. Essentially, you are measuring from the water's surface when filled to the very top of the vent well or the cell opening. A flash light may help when trying to see into the vent well.

Now take a ruler or measuring tape and measure from the mark you just made down to the bottom of the measuring device.

Alternatively, you can measure to the bottom of the battery vent well and add 1/4" to the total. Both should give you the same result.

Finally, select the Battery Water Level Indicator above whose fill height most closely matches the fill height of your specific battery to within 1/4".

2) Contacting the Battery Manufacturer
If you still have the maintenance manual that came with your battery, chances are it will contain the fill height or as it is often referred to as the "Water Reserve Capacity" of your battery. Most battery manuals can still be found online listed on the manufacturer's website.

Please note that all batteries, even in the same group size do not necessarily have the same water reserve capacity. Reserve capacity water levels vary greatly, so be sure to determine the correct water level reserve capacity for your specific make and model.

If you no longer have the maintenance manual that came with your battery, then it is time to call the manufacture. Make sure to right down the Model # of your battery prior to calling.

If you still have questions, feel free to contact us at any time at (419) 290-1103.


The Battery Water Level Indicator manufactured by Flow Systems works by way of our patented float system. One part of the float sits directly on top of the water inside your battery, while a red level indicator is visible to the user and extends above the top of the battery. As the water or electrolyte levels inside your battery evaporate, the float sitting on top of the electrolyte sinks in conjunction with the reduced water level. This is instantly reflected on exterior of the battery and visible to the operator.

There are two separate ways to gauge that you have the correct water level in your battery. Each side of the Water Level Indicator vent has two separate but distinct level markings. The first is a set of Maximum and Minimum designations. If your ultimate concern is simply to know when to add more water to the battery then, the max and min markings should be faced toward the user. If knowing the precise water level in battery, the user can view the opposite side of the indicator which contains a color gradient gauge, the shows a visual indicator that more water should be added and is approaching crucial levels.

The Battery Water Level indicator can be positioned in the battery cell vent hole so either of the visual indicators are facing in the direction that is most convenient for the operator or battery owner. Simply unscrew the vent by quarter turning clockwise, rotate the vent 180 degrees and re-insert back into the battery cell.

If you still have questions, feel free to contact us at any time at (419) 290-1103.


The short answer is 1/4" above the separator plates and 1/4" below the bottom of the vent well or anywhere in-between.

Correct Battery Water Level

It is important to note, that every battery has its own designated water level that is most appropriate for that make and model of battery. Even batteries in the same group size may vary from manufacturer to manufacturer. Its easy to maintain wet lead acid batteries if you understand the basics.

If you do not know the appropriate water level, the generaly held industry rule of thumb above should provide you the most appropriate water level for your battery.

The most important point to remember is that the plates inside your battery should be covered at all times. This includes during active use and during storage. There is a balance you try to achieve when watering your batteries. Too little water and it seems like you are watering constantly. Too much water and your batteries tend to have acid buildup on the surface of the battery.

So at the very least, the minimum water level should always be at least 1/4" above the plates however, you typically want to add more water than this. Keep adding water until the water level is just beneath the vent well tube. The vent well tube is the column that leads from the surface of your battery to the interior. Do not add so much water that it touches the bottom of the vent well. As gas is generated inside the cell, the pressure created needs some path to equalize with the outside environment. If the water level touches the bottom of the vent well, the pressure in the interior will forcefully bubble inside the vent well forcing the water to end up on the exterior.

Some batteries come equipped with slots in the vent well that allow for the gas generated in the cell to escape around the bottom of the vent well. The safe bet is always to only add water to within 1/4" below the bottom of the vent well.

If you still have questions, feel free to contact us at any time at (419) 290-1103.





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