Top 6 Best Battery Hydrometer Tools for Battery Testing (2019 Review)

Last updated on June 10th, 2019 at 09:03 pm

Although a voltmeter is a good tool to measure the state of charge of a lead acid battery, it is not necessarily the best approach. The most accurate way is to measure both the voltage and the specific gravity of the battery electrolyte. This gives you a holistic status of the battery. While voltage is measured using a voltmeter, the specific gravity can be measured using a battery hydrometer or a refractometer.

A battery hydrometer is a tool that uses the principle of bouyancy to measure the specific gravity of electrolyte in deep cycle batteries such as car batteries, golf-cart batteries, off-grid batteries, marine batteries among others. A user draws battery electrolyte sample using the battery hydrometer and takes the specific gravity readings from the scale on the tool. Some tools have temperature-compensated scales while others are not. Therefore, depending on the type of hydrometer you are using, you may or may not need to correct the SG readings for temperature variation. Once the readings have been made and temperature corrected, a voltage vs specific gravity chart from battery manufacturer is used to determine the actual state of charge and health of flooded battery. In this article we shall explore in details 6 of the best battery hydrometers you can consider to add to your deep-cycle battery maintenace kit.

6 Best Battery Hydrometers Comparison Table

MidNite Solar Hydrovolt HydrometerE-Z Red SP101 Battery HydrometerEditor'OTC 4619 Professional Battery Hydrometer s RatingKTI (KTI-70212) Battery TesterPerformance Tool W1657C Deluxe Battery TesterMighty Max Battery Hydrometer
might-max-battery-hydrometerMighty max battery hydrometer
Mighty max battery hydrometerMighty-max-battery-hydrometer
  • Has a temperature compensated scale
  • Compact size
  • Very high quality
  • Readings independent of vertical positioning of the instrument
  • Easy to read
  • Provides temperature compensated readings
  • Easy to take accurate readings from the pointer
  • Has a wide scale range from 1100 to 1300
  • Easy to read from the scale
  • Cheap and economical
  • Tough and unbreakable
  • Fitted with a thermometer.
  • Scale on the float has three colored sections; red,white, green.
  • Scale ranges from 1100 to 1300
  • Flexible rubber suction tube
  • One year warranty cover
  • Works on all 6-12-24 volt systems
  • Tests accurately the battery life
  • Works with a hot or cold battery
  • Detects overcharge
  • Made of plastic
  • Has a temperature compensated scale
  • Made of plastic
  • The scale on the float ranges from 1100 to 1300
  • Scale has three color coded sections (red, white, green)
  • Performs test on the battery in seconds
  • Does not have a temperature gauge.
  • Simple and easy to use

Lead-acid batteries are the oldest types of rechargeable batteries that are still very widely used for various electrical purposes. One of the applications is the 12V battery installed in many cars that store the electrical charge in form of chemical energy which is then converted to electrical energy and supplied to the ignition system and other accessories on demand. The other very common application these batteries is in the renewable energy industry – particularly the PV industry – for storing electrical energy generated by PV modules.

Lead-acid batteries are broadly classified into two categories: flooded type and sealed type. The flooded type is those whose electrodes are emersed in an electrolyte made of sulphuric acid and water. These batteries are vented to allow gases to escape during charging. As a result, the electrolyte levels and density fluctuate, making regular maintenance a necessity. The sealed type also referred to as the maintenance-free battery, does not require regular maintenance. During the routine maintenance of the flooded type batteries, a battery hydrometer is one of the essential tools that a technician should not leave behind. The tool is used to accurately determine the state of charge of a battery or cell. The following is a detailed review of six of the best hydrometers.

HydroVolt Battery Tester- MidNite Solar

If you are looking for a hydrometer that you can leave behind to your grandchildren, it is non other than the Hydrovolt battery tester. It is a German-made, compact-size, very high-quality chemical-resistant hydrometer that is accurate at all electrolyte temperatures. Its advanced design allows it to display temperature-compensated readings. Albeit a bit more pricey, the hydrovolt battery hydrometer is one of the most accurate battery testers. Its compact size allows it to be used on batteries that are hard to get at. It is also designed in such a way that the user needs not to hold it vertically or in any prescribed orientation to make accurate readings. The hydrovolt battery tester features a large, easy-to-read scale that has colored sectors that give a quick indication of the battery’s state of charge. It has a narrow, tightly-fitted tube that allows it to draw bubble-free fluid sample. The inside is fitted with a hydrostatic lock that prevents fluid loss and air bleed. In addition, its housing is made of sturdy,shock-resistant and non-corrosive plastic material that makes it survive accidental drops. Its pros and cons can be summarized as follows:

Advantages of HydroVolt Battery Tester

  • Large, easy to read, temperature compensated scale
  • Readings can be made without necessarily having to position the instrument vertically.
  • Very high quality
  • Because of the free-rotating rotor,the hydrometer is always level
  • Readings independent of vertical positioning of the instrument
  • Less likely to break when dropped compared to the conventional glass hydrometers

Disadvantages of HydroVolt Battery Tester

  • Its accuracy might be compromised if the rotors start failing.
  • More expensive than the conventional hydrometers.
  • Needs thorough rinsing to increase its durability
  • If you are accustomed to using the conventional hydrometer, you will find the squeeze bulb of this unit too small. That might be a little uncomfortable at first.
Although you spend a bit more on hydrovolt than on the ordinary hydrometers, the unit guarantees the most accurate readings. Its free-rotating rotor makes it level always. So, you dont need to hold it upright to make readings. Additionally, you dont have to mind about overfilling electrolyte and neither do you have to care about holding it upright. This is a perfect choice for any technician out there!

E-Z Red SP101 Battery Hydrometer

Characterized by its compact and lightweight design, E-Z Red battery tester is ideal for measuring the specific gravity of all deep cycle batteries ranging from the golf cart batteries to marine batteries. Because of its compact design, the battery hydrometer is particularly suitable for use on batteries that are installed in very tight spaces. The beautiful thing about this unit besides its size is the fact that the hydrometer readings are final and a user needs not to temperature-correct them. In other words, you can test your batteries at whatever temperature without the fear of making temperature-distorted readings.

Advantages of E-Z Red SP101 Battery Hydrometer

  • Provides temperature-compensated readings
  • Easy to take accurate readings from the pointer
  • Has a wide scale range from 1100 to 1300 to allow anyone to measure the specific gravity of any flooded lead-acid battery
  • Easy to read from the scale
  • Cheap and economical
  • Designed for garage use; tough and unbreakable
  • With a little more patience, the unit can be used as a battery filler
  • Includes a lifetime warranty

Disadvantages of E-Z Red SP101 Battery Hydrometer

  • Can not test motorcycle batteries because it requires more electrolyte than is available in the small batteries
  • Its small reservoir makes it unsuitable for use as a battery filler
  • Overfilling the hydrometer will give you false readings
  • Battery Hydrometer has to be held to level for accurate readings to be made
E-Z Red battery hydrometer, as its name goes, is easy to read. It has a clear scale that can be read without the user having to squint. However, it is difficult to make more accurate readings because the readings have a 25 points interval. If you are looking for a temperature compensated hydrometer that will access batteries installed in compact areas with not more than 8 inches clearance, E-Z RED is a perfect choice. It is undeniably one of the best and one of the most durable battery hydrometers you can find on the market that will also have a lifetime warranty cover.

OTC 4619 Professional Battery Hydrometer

If you are looking for a tool that measures both the specific gravity and the temperature-correction factor of battery electrolyte separately, then you should consider the OTC 4619 Professional Battery Hydrometer. It is a high-quality glass hydrometer fitted with a small thermometer. However, instead of the thermometer having a degree’s scale, it has a correction-factor scale. The user reads the correction factor and either adds or subtracts to the raw hydrometer readings. The float also has a clear, easy-to-read scale that makes it easy for a technician to make readings quickly.

Advantages OTC 4619 Professional Battery Hydrometer

  • Fitted with a thermometer for displaying temperature adjustment values for the hydrometer readings
  • The float has a scale that ranges from 1100 to 1300
  • The scale on the float has three colored sections: green, white, and red
  • The rubber suction tube is flexible thus offering easy access to the battery cells
  • The device is long enough to be used for any type of lead acid battery including the motorcycle and golf cart batteries.
  • The product has a 1 year warranty cover

Disadvantages OTC 4619 Professional Battery Hydrometer

  • Has glass components that can be easily broken.
  • Can not be put in the same toolbox with other heavy duty tools. It needs to be handled with care.
  • Overfilling with electrolyte makes the float hit the upper stopper causing it to give false readings.
  • Some people consider the readings on the scale too small to read from a distance
  • Does not ship with a carrying case despite its fragility
If you want to record raw hydrometer readings and temperature correction factor readings separately, the OTC 4619 Professional Battery Hydrometer is a suitable choice. However, you must be extra careful with this unit because of its fragility.

KTI (KTI-70212) Battery Tester

The KTI-70212 battery hydrometer is similar to the E-Z Red SP101 except that they differ a bit in shape and design. It displays temperature-corrected hydrometer readings which makes it ideal for testing extremely hot or cold battery electrolyte. The unit has a curved nozzle that allows it to be used in hard to access places. However, the rubber suction tube tends to kink when battery fluid is drawn while holding the hydrometer in an upright position. However, the kink aids in closing off the hose if you wish to withdraw it from the battery to read it. The unit also has a lifetime warranty, which is what any buyer wants from any product.

Advantages of KTI-70212 Battery Tester

  • Works on all 6-12-24 volt systems
  • Tests immediately and accurately the battery life
  • Works with a hot or cold battery electrolyte because it displays temperature compensated values
  • Made of plastic hence more durable than glass tube battery testers
  • Small and compact
  • Easy to read scale
  • Has a lifetime warranty

Disadvantages of KTI-70212 Battery Tester

  • Accuracy of hydrometer readings is dependent on vertical positioning of the tool
  • Failure to rinse the tool well with fresh water may lead to faster deterioration

Performance Tool W1657C Deluxe Battery Tester

Advantages of Performance Tool W1657C Delux Battery Tester

  • Has a temperature compensated scale
  • Made of plastic thus more durable than glass hydrometers

Disadvantages of Performance Tool W1657C Delux Battery Tester

  • Requires to be held upright in order to make accurate readings.
  • Needs to be rinsed well with fresh water to prevent it from deteriorating quickly

Mighty Max Battery Hydrometer

Sometimes when working in areas that don’t experience extreme weather, all you need is a simple battery tester. The mighty max battery hydrometer is certainly the tool you might want to add to your tool chest because of its simple design. It is only meant to show raw hydrometer readings that are not temperature-adjusted. The tube is made of plastic to increase the tool’s durability. In addition, to avoid getting false readings due to overfilling, the tube is not fitted with a stopper at the bulb’s head. Therefore, the float can rise into the bulb to allow a user make readings without worrying about overfilling.

Advantages of Might Max Battery Hydrometer

  • The scale on the float ranges from 1100 to 1300
  • The scale is color-coded to make it easier to read and deduce battery state of charge quickly
  • Performs test on the battery in seconds
  • Requires a thermometer to measure temperature separately in order to compute temperature adjustments on the specific gravities
  • Simple and easy to use
  • Bulb can be pushed all way down to create more storage space in your toolbox.
  • Does not have a rubber stopper at the head of the bulb, which allows the float to rise into the bulb itself.

Disadvantages of Mighty Max Battery Hydrometer

  • Shows raw hydrometer readings that are not temperature-compensated
  • Plastic tube is less clearer than glass tube
  • Unreliable for testing too cold or too hot battery electrolyte.

What is a hydrometer?

The dictionary meaning of a hydrometer (also known as an areometer) is simply an instrument or a tool that measures the specific gravity of liquids. Specific gravity is the measure of how many times a liquid is denser than water. For example, you can use a hydrometer to measure how many times sulphuric acid or alcohol is denser than water. The most common industrial use of a hydrometer is to measure the density of the electrolyte in flooded lead-acid batteries to determine the state of charge. When the battery is fully charged, the concentration of sulphuric acid is high hence a high specific gravity. As the battery discharges, the electrolyte becomes weaker (becomes less acidic) hence a low specific gravity. There is a linear correlation between the state of charge and the specific gravity of the electrolyte. The correlation is so accurate that a hydrometer test is often considered the ultimate measure of a battery’s state of charge. You can use it to diagnose your car battery if, for example, it runs flat quite often or it does not work as well as it used to.

How to use a battery hydrometer

A typical glass battery hydrometer has, at least, the following parts: a rubber suction bulb, a glass viewing tube, a glass float, and a rubber suction tube. Some of the most advanced hydrometers are fitted with thermometers to allow you to read both the temperature and the specific gravity of the electrolyte for hydrometer correction. The first step before using a hydrometer is to ensure that all parts are properly assembled. The following is a procedure for assembling a hydrometer:

How to assemble a typical battery tester

  1. Fit the rubber stopper to the head of the glass viewing tube.
  2. Fit the rubber suction bulb to cover the rubber stopper.
  3. Hold the glass tube by the suction bulb and tilt it vertically.
  4. Insert the float into the tube with the scaled end first
  5. Fit the rubber suction tube.
  6. Ensure that both the suction bulb and suction tube are tightly fitted.

All flooded batteries work on the same principle. However, since the most common application of deep cycle batteries besides the photovoltaic industry is the auto industry, the following procedure will illustrate how to test a typical car battery. Note that the procedure applies globally to all flooded-type lead acid batteries.

How to test a car battery using a battery hydrometer

    1. Begin with assembling the hydrometer parts.
    2. Open the vent cap of the deep cycle battery cell and dip the rubber suction tube

Warning: If the level of battery electrolyte is below the plates, use a battery filler to top off battery water until the battery plates are covered.

  1. Squeeze and release the rubber suction bulb to draw the electrolyte into hydrometer
  2. If your hydrometer is fitted with a thermometer, draw the electrolyte several times so that the thermometer can adjust to the electrolyte temperature
  3. Draw enough electrolyte into the hydrometer to allow the float to rise up freely without contacting the top and the bottom.
  4. Allow the float to seek its own level
  5. Note the readings then drain the electrolyte from the hydrometer.
  6. Move on to another cell and repeat steps 2 to 7

Note: The specific gravity of the electrolyte in an aged battery tends to decrease at full charge. However, there is no reason to replace the battery as long as the specific gravity readings of each cell are within 50 points to each other.

How to read a hydrometer

A battery hydrometer has a specific gravity scale. Some scales range from 1100 to 1300 while others range between 1000 and 1300. The specific gravity of a fully charged battery should read 1300 while a fully discharged battery should read 1100 or below.

Procedure for reading a battery hydrometer

  1. Suction the electrolyte using the procedure outlined above
  2. Hold the hydrometer in an upright position and allow the float to settle.
  3. Take the reading by viewing the scale through the sample
    electrolyte, and adjusting your line of sight until it is in the plane of the horizontal electrolye surface.
  4. Take the reading of the bottom meniscus of the electrolyte.
  5. Do not take the reading if the float is touching the top or bottom of the hydrometer’s glass viewing tube.

How to Perform Hydrometer Temperature Correction

The specific gravity of liquids tends to be affected by temperature. This phenomenon is derived from the fact that materials expand when heated. As a result, their volume increases consequently causing the density to decrease. Due to the decrease in density of the liquid, their specific gravity decreases. The opposite is also true; a decrease in temperature will cause the specific gravity of liquid to increase. The specific gravity of battery electrolyte decreases by 0.002 for every temperature increase by 5 degrees Fahrenheit above 80 degrees. Similarly, it decreases by the same value for every decrease by 5 degrees Fahrenheit below 80 degrees. With this in mind, it is always important to arm yourself with a thermometer or a temperature gauge whenever you are conducting the battery hydrometer test. This allows you to measure the temperature of the electrolyte and conduct hydrometer temperature correction accordingly. You can use the two methods discussed below to temperature-correct your specific gravity readings for accuracy:

    1. Using a hydrometer correction table/chart
  1. Manual calculation using the hydrometer temperature correction formula

I. Hydrometer correction using a Hydrometer Temperature Correction Table

A hydrometer temperature correction chart or table is a very handy cheat-sheet that helps determine the correction factor. It has two columns; one bearing the temperature in Fahrenheit and the other column populated with the Hydrometer Correction factor. For every 5 degrees Fahrenheit above 80 degrees F, there is an addition of 0.002 to the specific gravity readings. Similarly, for every 5 degrees F below 80 degrees F, there is a subtraction of 0.002 from the actual SG. Upon the determination of the temperature of each sample of electrolyte, you can make temperature adjustment to your specific gravity readings before recording. The table helps simplify the temperature correction exercise, which can otherwise be time-consuming if you have to perform the calculations manually for each sample.


II. Manual calculation using the Hydrometer Temperature Correction formula

Sometimes you might not have the hydrometer temperature correction table and you may want to make the temperature adjustments to your raw hydrometer readings. The alternative way to do it is by manually calculating the correction factor using the hydrometer temperature correction formula and then add or subtract it to your actual raw hydrometer readings. The example below shows how to use the formula to manually temperature correct raw battery specific gravity readings.

How to calculate the correction factor using the hydrometer temperature correction formula: Example

Assume it is during the summer and your hydrometer reads 1230 while your thermometer reads 100 degrees Fahrenheit. The temperature corrected specific gravity would be:

  1. Actual Specific gravity: 1230
  2. Temperature: 100 Degrees F
  3. Temperature difference: 100 deg – 80 deg = +20 degf
  4. Correction factor: {(20 deg/5 deg) * 0.002} = +0.008
  5. Corrected Specific gravity value: 1230 + 0008 = 1238

Another example is when you are in an extremely cold environment such as during the winter. Assume your hydrometer reads 1230 while your thermometer reads -10 degrees Fahrenheit. The temperature corrected specific gravity would be:

  1. Actual Specific gravity: 1230
  2. Temperature: -10 Degrees F
  3. Temperature difference: -10 deg – 80 deg = -90 degf
  4. Correction factor: {(-90 deg/5 deg) * 0.002} = -0.036
  5. Corrected Specific gravity value: 1230 – 0036 = 1194


As you can see from the two examples above, the temperature of an electrolyte can significantly distort the actual specific gravity readings. For instance, a potentially dead cell can appear good in extremely cold temperature while a good battery may seem bad at high temperatures. For that reason, it is very critical to have a thermometer with you while using the simple battery hydrometer such as the Mighty Max Battery Hydrometer. A thermometer measures the temperature of the electrolyte so that you can calculate the appropriate correction factors that will be used to temperature-adjust you SG readings. Alternatively, you can purchase the more advanced battery hydrometers that come fitted with a thermometer. The OTC 4619 Professional Battery Hydrometer is an ideal example of a battery hydrometer that allows you to simultaneously record both the SG and temperature readings as well as the corresponding correction factor. Otherwise, you can opt to buy the hydrometers that are internally built to provide temperature compensated readings. The E-Z Red SP101 Battery Hydrometer is one of the best types of temperature-compensated hydrometers. It displays specific gravities that are already temperature-adjusted. While using this type of hydrometer, you don’t need to carry a temperature gauge and neither do you have to record the temperature of the electrolyte. It is one of the most accurate, though pricier, type of a battery hydrometer.

A battery hydrometer, like any other tool, will accidentally fall. However, unlike most tools, when a glass hydrometer hits hard on the ground, it will most definitely break. Actually, most hydrometers (especially the glass hydrometers)are more likely to break than malfunction. With that in mind, it is important to consider the physical material and design of a hydrometer as you look at other features. Plastic battery testers such as theKTI (KTI-70212) and the Performance Tool W1657C Deluxe Battery Testers are less fragile and will last longer than the glass hydrometers.

How to Use a Battery Hydrometer – Video

Frequently Asked Questions (FAQ)

What does a battery hydrometer do?

A battery hydrometer is a battery testing tool used to check the specific gravity of the battery electrolyte to determine the state of charge of a battery.

How does a hydrometer work?

A hydrometer, whether for testing battery electrolyte, beer, or any other fluids works on the principle of buoyancy. The tool usually has a floating element that rises depending on the density of the fluid being tested.

How do you check the specific gravity of a battery?

When you suck the battery electrolyte with a hydrometer, the float will rise or rotate (depending on the construction of your unit). When the float settles, you will read the value from the scale where the pointer points. If your unit is the conventional model, you will have to hold it upright and read the level of fluid at the meniscus.

What is the specific gravity of a battery?

The specific gravity of a good battery may range between 1100 to 1300 depending on its state of charge. Hydrometer readings below that range indicate a dead battery.

What is the specific gravity of a fully charged battery?

The battery electrolyte of a fully charged battery should have a specific gravity above 1250. In other words, the electrolyte should be 1.25 times denser than water.

How do you know if a car battery is no good?

You can tell that a car battery is not good by checking the specific gravity of electrolyte with a hydrometer. You should start to worry if it reads anything below 1100. You can also tell that a battery is not good by how long it keeps the charge. For example, if your car battery goes flat more frequently then that is a sign of a bad battery. You can also use a battery load tester to test how long a battery lasts with a given load. If it discharges really quick then you should start planning for a replacement.

What fluid do you add in a car battery

You add distilled water in a car battery. The purpose of distilled water is to replenish lost water through gassing. By adding the correct amount of distilled water to a battery, the ratio of water to sulphuric acid needed for optimal operation is maintained.

How do you check the electrolyte level of a battery?

You can check the electrolyte level by visual inspection or by dipping the tip of a hydrometer.

How do you add electrolyte to a battery?

The most effective way to add electrolyte to a battery is using a battery filler with automatic shutoff. The filler only tops off distilled water to the required level without underfilling, overfilling, or spilling.

What level do you top up your battery up to?

For golf cart batteries that typically have a clear casing, you add water to the upper-level mark on the side. For other lead-acid batteries, it is a thumbs rule to fill up to about 1/8″ below the bottom of the vent hole.

Can you use bottled water for a car battery?

No. You cannot use bottled water because it contains impurities that may damage the battery. Only distilled water should be added to the battery.

How many volts is a 12V battery fully charged

Each cell of a healthy, fully-charged lead-acid battery supplies between 2.14V and 2.2V. This is equal to 12.8V on the lower side and 13.2V on the upper side for a typical fully-charged 12V battery.

What is the SI unit for specific gravity?

Specific gravity is unitless. It is simply the measure of how heavy fluid is compared to water.


An electrical engineer by profession who used to work at a solar microgrid firm as an O&M supervisor. There, he realized that having the right tools for the trade is equal to getting the job half done. That's what inspired him to start this website!

4 thoughts on “Top 6 Best Battery Hydrometer Tools for Battery Testing (2019 Review)

  • July 7, 2018 at 6:01 am

    I am inspired by your work and got some great ideas. It really gives me information that I am looking for. Thanks and keep sharing 🙂

    • July 7, 2018 at 7:11 am

      You are welcome Joshua! You can share it to your social space and also let me know about your experience with hydrometers. 🙂

  • August 12, 2019 at 11:53 pm

    Guy at Advance told me hydrometer test is invalid. All my cells are in the red. His fancy tester just said the battery needs charging. (It said it still had sufficient cranking amps, but voltage was low.) He said the battery was “maintenenance free” even though you can pop off the cap and see the electrolyte solution (and test using hydrometer). Is there any truth to what he is saying?

    • August 14, 2019 at 3:04 am

      Hello Lee,
      First off, thanks for reaching out. Second, “maintenance free” means that you cannot add water/acid to battery. Therefore, if your battery is labelled as so, I would expect that the top is sealed to prevent topping off. Otherwise, if the top is can be opened, whether or not the battery is labelled “maintenance free”, it means to me that you can check electrolyte level and probably top it up. A hydrometer can also be a handy tool for checking the health of the cells. In your case, if the voltage is low and the electrolyte is in the “red” zone, then it is possible that it only needs charging. I would, therefore, advise that you crank up the car and leave it running or drive around for some time so that the alternator can charge up the battery. Afterwards, make sure to measure the voltage and probably do a load test. If the problem persists, you may consider replacing the battery; it may be getting old.


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