5 Best Battery and Coolant Refractometer Testers

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A good alternative device to a battery hydrometer is a battery refractometer. This measuring device is safer and measures specific gravity of battery electrolyte and other fluids more accurately. Unlike a hydrometer that uses the principle of buoyancy to measure fluids, a refractometer operates on the principle of refraction to determine the specific gravity of liquids. As you probably know, the refraction of light is simply the bending of light that occurs when a ray of light passes from one medium to another. This bending is measured using a unitless value called the index of refraction which is simply the ratio of the sine of the angle of incidence of light and the sine of the angle of refraction.

How a refractometer works

A refractometer has a measuring prism on which you place a drop or two of the liquid you want to measure. The prism has a clear cover that spreads the liquid and allows light to pass through. When a ray of light hits the prism through the illuminator cover, it bends. The angle of bending depends on the density of the liquid sample.

This optical bending of light occurs due to the slowing of the velocity of light when it passes through a dense medium. The refraction of light increases with density. This principle of refraction is what a refractometer uses to measure the specific gravity of liquids.

However, the advantage of a refractometer is that it shows the density readings in a less quirky manner that is easy to read and interpret. When you place your eye on the eyepiece, you see a density graph showing the density level of your liquid. You only have to ensure that there is enough illumination on the prism to see the readings more clearly.

In this article, I will explore in great detail the 5 best battery refractometer units. These refractometers also double up as glycol testers for measuring the concentration of ethylene-glycol and propylene-glycol based radiator antifreeze fluids. This add-on feature on these optical tools allows car owners and auto mechanics alike to not only keep the battery in check but also the cooling system. Furthermore, some of the battery refractometers in this review can also measure the concentration of windshield washer fluids. This feature is also very useful because it helps to maintain the correct concentration of the windshield washer. A proper concentration of windshield fluid is effective and does not freeze during the extremely cold season such as winter.

Let’s now explore the refractometer units.

Best Coolant and Battery Refractometers Comparison Table

Aichose 3-in-1 Antifreeze Tester in Fahrenheit ScaleRobinair Coolant and Battery RefractometerTRZ 4-in-1 Refractometer for antifreeze liquids and battery electrolyteExtech RF41 Portable Battery Coolant/Glycol RefractometerAde Advanced Optics ATC Glycol Antifreeze/battery Fluid Refractometer
trz-4-in-1-Refractometer-Ethylene-Glycol-Propylene-Glycol -n-antifreeze
Users' Ratings
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  • Measures the freezing point of ethylene glycol or propylene glycol based automobile antifreeze coolant.
  • Also measures concentration of those coolants.
  • Determines the specific gravity of battery electrolyte.
  • Has three scales: specific gravity scale (1100 - 1400), ethylene glycol scale, and propylene glycol scale.
  • Has 3 scales for measuring battery fluids, ethylene glycol coolants, and propylene glycol coolant blends.
  • Coolant scales are in Fahrenheit
  • Features an automatic temperature compensation mechanism
  • The specific gravity scale ranges from 1150 to 1300 with a resolution of 0.01 sg
  • The temperature scale has a resoultion of 10 degree F
  • Measures specific gravity of battery electrolyte
  • Determines the freezing point of ethylene glycol and propylene glycol based antifreeze coolant.
  • Also measures and checks Windshield Wiper Fluid
  • Has 4 scales for measuring four types of fluids: battery acid, washer fluid, antifreeze liquids, and urea solution.
  • Temperature scale is in fahrenheit.
  • Built with automatic temperature compensation feature
  • Just 2-3 drops of electrolyte or radiator antifreeze needed
  • Measures the specific gravity of battery acid from 1110 to 1300
  • Also measures freezing point of Propylene/Ethylene Glycolin from -50°C to 0°C.
  • Has an easy-to-read scale
  • The automatic temperature compensation from 10°C to 30°C feature is integrated.
  • The prism and lens have a simple focus adjustment.
  • Measures freezing point of Propylene or ethylene glycol
  • Has multiple scales for measuring ethylene, propylene glycol, and brake fluid.
  • Temperature scale is in degrees fahrenheit
  • Also measures the specific gravity of battery acid
  • Has automatic temperature compensation for temperatures between -60 Deg F and 32 Deg F.
Parts Included Firm plastic case
Cleaning cloth
Suction tube
Screw driver
Operating instructions
Rigid foam-lined plastic case
Cleaning cloth
Screw driver
Vial of distilled water
Plastic case
Cleaning cloth
Suction tube
Screw driver
Operating instructions
Tool with case
Calibration screwdriver
Plastic pipette
User manual
Cloth case
Calibration screwdriver
Plastic pipette
User's Manual
Temperature Scale -84°F - 32°F for ethylene glycol and -60°F-32°F for propylene glycol -60° F to 32° F for antifreeze coolant -60°F-32°F -60° F to 32° F -60° F to 32° F
Specific Gravity Scale 1.100 - 1.400 1.150 - 1.300 1.100 - 1.400 1.150 - 1.300 1.110 - 1.400
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Refractometers Detailed Reviews

Aichose 3-in-1 Battery Acid and Coolant Refractometer Review

The Aichose 3-in-1 refractometer is a high precision optical instrument used to test antifreeze coolants and battery electrolyte. It comes in a nice hard plastic case with tools to clean and adjust if necessary. Among the three parameters the aichose refractometer measures are 2 properties of ethylene glycol or propylene glycol based automobile antifreeze coolants and the specific gravity of battery acid. This his why it is referred to as 3-in-1 refractometer.

Features of Aichose refractometer

Aichose refractometer features high quality optics with ultra smooth focusing including an optical lens that has a high refractive index for high precision. All these are protected under a durable aluminum alloy body. When you view through the view finder, you see three different scales: the specific gravity scale, the temperature scales for the two types of coolants, and the glycol concentration scale. The temperature scales are in Fahrenheits, concentration scale in percentage, and the specific gravity scale is unitless and ranges from 1100 to 1400.

Battery acid is very corrosive. However, the materials used to build the aichose refractometer are resistant and therefore do not corrode with acidic or alkaline solutions. This makes the instrument a perfect choice for use to check the strength of battery electrolyte and for measuring glycol levels even in hydronics heating systems. The storage of this instrument is nothing to worry about because it has a compact sturdy plastic casing that protects it from impact.


  • The body is made of aluminum alloy for increased durability.
  • It is resistant to abrasion and corrosion
  • Requires only 2 to 3 drops of sample
  • Convenient for use at different temperatures because of its automatic temperature compensation feature.
  • Performs three different functions
  • Sturdy carrying case
  • Fairly priced
  • Covered by full 12 months replacement warranty.


  • None


In a nutshell, Aichose 3-in-1 refractometer is a very useful, easy-to-use optical instrument that performs three important functions that help to keep your car engine and flooded battery in good condition. It is accurate, sturdy, and won’t cost you a tooth and a nail.

Robinair Coolant and Battery Refractometer Review

This is another optical refractometer for glycol, antifreeze, coolant, and battery acid. It has a solid construction and comes packed together with other accessories in a hard plastic carrying case. The instrument is equally easy to use and has easily readable scales for making accurate readings. In addition, the tool has a smooth focus adjustment to enhance viewing and a vial of distilled water for tool calibration.

Features of Robinair coolant tester

The robinair refractometer measures three different types of liquids. It measures the freezing point of ethylene glycol blends of antifreeze as well as propylene glycol blends. It also measures the specific gravity of battery electrolyte in flooded batteries. Each of these fluids has a temperature compensated scale from which to read.

Unlike the Aichose refractometer, robinair displays temperature in ° F. The temperature ranges from -60° F to 32° F. The specific gravity scale, on the other hand, ranges from 1.15 to 1.3. Together with its high quality optic, the tool has an ultra smooth focusing that makes reading the scales very easy. This makes it a great multipurpose tool for determining the freezing point of radiator antifreeze and for checking the strength of charging fluid in flooded batteries.


  • Made with rugged aluminum housing protects the internal components.
  • Has an easy to read scale
  • The ATC guarantees temperature compensated refractometer readings
  • Ultra smooth focusing
  • High quality optics
  • Made in the U.S.A.


  • Quite expensive


Generally, the Robinair refractometer, though pricier, well built and great optical instrument for testing coolants and battery acid. Moreover, it is made in the U.S.A and includes additional accessories. It also comes packaged in a nice rigid plastic carrying case that is durable enough to withstand life in a toolbox.

TRZ 4-in-1 Antifreeze Tester Review

This instrument as well has a solid sturdy construction with an aluminum alloy body for imcreased durability. Its optical components including the prism are made of materials that are resistant to abrasion and corrossion to allow them work with acid and alkaline solutions. This measurement tool features a focus adjustment and a rubber grip just like the rest of the refractometers reviewed thus far. In order to ensure that the readings are not affected by temperature variations, this optical instrument features an automatic temperature compensation for temperatures between 32 degree F to -60 degree F

Features of TRZ antifreeze tester

The Hamh Optics&Tools 4-in-1 portable refractometer combines functions: 1) checks the health of battery electrolyte, 2) determines the freezing point of ethylene and propylene glycol automotive coolants, 3) measures the freezing point of windshield washer fluids, and 4)determines the concentration of urea in AdBlue (a solution of water and urea used to lower emissions in diesel powered engines). The scales for measuring the freezing point of engine coolants are in Fahrenheits and range from -60° F to 20° F with a resolution of 5° F while that of screenwash fluid ranges from -40° F to 15° F. The scale for AdBlue, on the other hand, is in percentage and ranges from 30% to 35% with a resolution of 0.19%.


  • Has most functions; 4 distinct functions
  • Has a 2 year warranty Free Replacement Guarantee
  • Cheapest


  • Carrying case is not robust enough to protect the instrument from heavy impact.


If you are looking for a portable optical tool that will not only measure the freezing point of antifreeze liquids and sniff out bad batteries, the Hamh Optics & Tools 4-in-1 battery refractometer is a great choice. It will also measure the concentration of AdBlue to ensure that you get the right concentration which will break down harmful exhaust gases from your diesel-powered engine. In addition, this tool will also measure the freezing point of screenwash fluid. The only downside is its less robust plastic carrying case that may not effective protect the instrument from impact. Other than that, the tool is affordable and great to have in place of a hydrometer.

Extech RF41 Portable coolant and Battery Refractometer Review

The Extech RF41 portable battery acid and coolant refractometer is a high precision optical instrument from Extech company. It measures the freezing point of automotive coolants and the specific gravity battery electrolyte. It is easy to operate and has an quick to read scale for specific gravity readings and the freezing point temperature in degrees celcius. It also comes packed nicely in a solid plastic carrying case that stows away nicely in a tool box.

Features of Extech RF41 refractometer

Extech RF41 is built with high quality and non-corrosive optics and requires only 2-3 drops of sample for fast and accurate readings. It also features an automatic temperature compensation from 10° C to 30° C to ensure that the readings are as accurate as possible. However, it only has 2 scales; the specific gravity scale ranging from 1150 to 1300, and the temperature scale for ethylene glycol/propylene glycol ranging from -50°C to 0°C.


  • Easy to use and calibrate
  • The tool has an easy to read scale
  • Stows away nicely in a tool box in its carrying case
  • Includes a 1 Year Warranty cover
  • ATC ensures accurate refractometer readings


  • A bit pricey.
  • The scale ranges from 1150 to 1300


Extech RF41 refractometer is a high performance optical instrument from Extech company. It works well for measuring the freezing point of automotive coolants, glycol in chiller systems, hydronic and free cooling systems among others. The exceptions, however, are that the instrument does not measure concentration percentage of glycol, its automatic temperature correction does not cover lower temperature, and that the instrument is quite expensive.

Ade Advanced Battery Acid and Glycol Meter Review

Ade advanced optics refractometer is a portable precision instrument for measuring the freezing point of ethylene or propylene glycol based coolants. It is very similar to the other competitors as far as the compact aluminum alloy body construction is concerned. It is also made of high quality optics with smooth focusing for accurate measurements. In addition, the components are resistant to corrossion allowing it to perfectly work with acidic and alkaline solutions.

Ade Advanced refractometer features

The hand refractometer is capable of measuring three different properties of fluids. In other words, it can be used to check the strength of battery elctrolyte, determine the freezing point of automotive coolants as well the concentration of ethylene or propylene glycol antifreeze in water by percentage. Like the other units, this refractometer has an automatic temperature compensation for temperatures between 32 degree F to -60 degree F therefore allowing you to make accurate measurements.


  • Free replacement guarantee within the warranty period
  • Requires only 2 to 3 drops of sample
  • Aircraft aluminum body and premium optical lens make the refractometer durable
  • Also checks brake fluid for water absorption
  • Fairly priced
  • Has a 2 years warranty cover


  • Comes in a cloth carrying case which won’t protect the instrument from impact


Ade Advanced Refractometer is a great tool for in-depth analysis of lead acid batteries. It is good for testing golf cart batteries and flooded batteries of your offgrid system because it provides more accurate specific gravity readings than a hydrometer and is quick to read. It also measures the freezing point of engine coolants and displays the temperature in Fahrenheits. In addition, this tool can be very handy in determining the concentration in percentage of ethylene/propylene glycol based solutions. The downside, however, is the cloth carrying case that does not protect the fairly delicate tool from impact.

Why Check the Engine Coolant Concentration?

Most car owners know the importance of measuring the sg of battery acid but quite a good number of them don’t understand why keeping the engine coolant concentration in check is important, especially during winter and summer. This is the reason: When you have the correct water-coolant ratio in your cooling system, the coolant remains in liquid form even in very cold temperatures. Similarly, in very hot temperatures, the coolant takes in more degrees before turning into vapor. This extends protection on the engine and the cooling system throughout the harsh seasons.

On the other hand, when you have the wrong antifreeze mixture concentration, the coolant freezes easily at low temperatures. When you start the car, the frozen coolant particles get thrown around inside the engine and the cooling system. This may cause catastrophic damage to the engine resulting in a very expensive fix. Similarly, in very hot temperatures, the incorrect glycol mixture in the radiator transfers heat from the engine very poorly, causing the engine to overheat. Again, overheating your engine shortens its life significantly. This is why a coolant refractometer or a battery refractometer with a glycol meter is a very handy tool for every car owner and auto mechanics. With it, you can never go wrong with the concentration of important automotive liquids and your car will thank you for that! Your battery as well will give you some extra cold-cranking amps (CCAs) and you will be happy.

How to Use Battery Refractometer

Time needed: 5 minutes

Follow these 10 steps to determine the health or state of charge of lead acid deep cycle battery using a battery refractometer. You can follow the same steps to use a glycol refractometer to test antifreeze coolant concentration.

Required Items:

i. Battery refractometer

ii. Pipette

iii. Distilled water

iv. Soft cleaning cloth

v. Rubber gloves

vi. Safety goggles

  1. Wear safety equipment

    Battery acid and other machine fluids are dangerous. So, safety comes first!. At a minimum, put on safety goggles, rubber gloves, and closed work shoes.

  2. Clean the refractometer

    Ensure the Refractometer is clean before using it. Otherwise, rinse it using RODI water and wipe using the supplied soft cloth

  3. Check refractometer calibration

    Confirm that the instrument is properly calibrated. If not, jump to the next section first.

  4. Collect sample using a pipette

    Suck the sample to be tested with a pipette. The sample can be battery electrolyte, engine coolant, AdBlue, or windshield wiper fluid.

  5. Place sample of the refactometer prism

    Place a few drops of sample you collected with a pipette on the prism lens or view area and allow it to cool for 30 seconds.

  6. Cover the prism

    Put the prism cover plate back in place carefully.

  7. Look through the view finder

    Place one eye on the view finder and and look through. You will see a line marking the split between a white and blue area. If you are having a hard time seeing the markings clearly, turn the focusing ring on the eye piece until it clears up.

  8. Read the scale and record readings

    Read the respective scale depending on the type of sample. For battery acid, use the specific gravity scale, and for automotive coolant, use the antifreeze scale. Do the same for AdBlue and Screenwash fluid. If if you are testing electrolyte of flooded battery, repeat the process for each cell and record the readings.

  9. Inteprete readings

    Use a coolant concentration chart to intepret coolant refractometer measurements. For battery, use an electrolyte chart to find out the health of each cell or the state of charge of the battery.

  10. Rinse refractometer and store safely

    Rinse battery electrolyte and antifreeze coolant from the refractometer using distilled water or RODI water. Then wipe with the soft cleaning cloth. Once the optical instrument is clean, store it back together with its accessories in its carrying case.

How to Calibrate a Refractometer for Machine Coolants and Battery Acid

In order to properly calibrate a portable handheld refractometer, you need at a minimum the following five items:
1) RODI water
2) 35 part calibration solution
3) Flat head screwdriver
4) Soft cleaning cloth
5) User manual
Once you have all those in place, use the following procedure to successfully calibrate a refractometer.

  1. Open the cover plate and check the prism for any finger prints, dust, dirt, or debris
  2. Wipe the view area clean.
  3. Rinse the refractometer with RODI water.
  4. Remove the rubber cover of the calibration adjustment screw.
  5. Add refractometer calibration fluid on the prism evenly and place the cover.
  6. Let the refractometer sit for about a minute to allow the calibration solution to adjust to the temperature of the refractometer.
  7. Hold the refractometer to a bright source of light and read the scale. The bright light lets you see the measurement lines more clearly.

Maintenance Tips for a Battery/Antifreeze Refractometer

A portable handheld refractometer is a fairly delicate optical instrument that requires care and regular maintenance to keep working optimally and effectively. The following are some of the care and maintenance tips for a battery and antifreeze refractometer.

  • Protect the glass prism from scratches

    Scratches and chips can greatly affect how light enters the refractometer and ultimately affect the accuracy of measurements. It is therefore important to protect the optical instrument from damage to ensure that you are always getting the most accurate readings possible.

  • Proper storage

    Always make sure you store the tool back into its protective case after use because slight drops and bumps can dislodge or move the refractive mirrors inside.

  • Rinse and clean

    It is good practice to always rinse and clean your refractometer after use to ensure that your readings are always correct. This also makes the tool always ready for use every time you want to use it thus saving time.

  • DO NOT Touch the optical surface of a refractometer

    If you have to touch the optical surface, use very clean non-abrasive gloves. Otherwise, mishandling will affect the accuracy of this high precision optical instrument.

Frequently Asked Questions (FAQ)

What is a refractometer?

A refractometer is an optical instrument that uses the concept of bending of light by fluids to determine various properties such as freezing point, concentration, or specific gravity of a sample fluid.

What does a refractometer measure?

A refractometer in the automotive industry can measure the freezing point, concentration, and specific gravity of different types of industrial fluids. For example, you can use it in place of a battery hydrometer to measure the strength of battery acid. You can also use it to measure the freezing point or concentration of ethylene or propylene glycol-based antifreeze coolants such as Dexcool. Some even measure the concentration of AdBlue fluids and the freezing point of windshield fluids. Keeping the vehicle fluids from freezing protects your car during arctic climate such as in the winters. For instance, the frozen coolant in the cooling system of your car can severely damage the engine.

How do you read a refractometer?

To read a refractometer, you place your eye on the eyepiece and through the viewfinder, you will see a line marking a split between a white and blue area. You then read the desired measurement from the respective scale. However, if the scale is not clear enough, you can increase the illumination on the prism and turn the adjustment ring to achieve a fine focus.

What is the difference between a battery hydrometer and a battery refractometer?

The main difference lies in the principle upon which both units operate. While battery hydrometers rely on the principle of buoyancy, a refractometer uses the property of refraction or rather the bending of light when it passes through fluids. Another difference is the amount of sample needed for each tool. A refractometer only needs 2 to 3 drops of sample whereas a hydrometer needs enough amount of sample to carry the float.

What is the ratio of coolant to water?

Ideally, the correct ratio of coolant to water is 50:50. However, any ratio between 40:60 and 60:40 is safe for your car.


Hey there! I am an field electrical engineer by day, a blogger by night, and DIYer on weekends. Throughout my career, I have used many tools and learned that getting the right tool for the job is the first step to getting the job done right. This is why I write about tools and tests/reviews them on this blog.

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