How To Know Conditions Of A Car Battery Using The Heavy Load, Hydrometer Load & Open Circuit Voltage Test

How To Know Conditions Of A Car Battery

How To Know Conditions Of A Car Battery
How To Know Conditions Of A Car Battery

How To Know Conditions Of A Car Battery Using Hydrometer

The hydrometer is an instrument used to test the state of charge of a battery. The state of charge of a conventional lead-acid battery can be determined by testing the specific gravity of the electrolyte.

Do not, however, make the hydrometer test immediately after water has been added to the electrolyte.

Measurement should be made before the water is added in order to obtain on a representative sample. If the level is too low to obtain, a sample water should be added as needed.

After the battery has been used long enough to thoroughly mix the water with the electrolyte, the sample may be taken with a hydrometer.

To read hydrometer, squeeze bulb to draw enough electrolyte from cell to raise float.

The float should not touch barrel of the hydrometer.

Release pressure on a bulb and observe specific gravity reading on a float.

Check thermometer and compute temperature-corrected specific gravity of the electrolyte.

How To Know Conditions Of A Car Battery
How To Know Conditions Of A Car Battery

How To Know Conditions Of A Car Battery Using Heavy Load Test

In heavy load test which is also called ‘high rate discharge’ or ‘capacity test’, it is a good test of the battery’s ability to perform under load.

In this test, a good battery will produce current equal to 50 percent of its cold cranking rating for 15 seconds and still provide minimum voltage to start the engine.

Steps To make the heavy load test:

  1. Charge battery, if necessary, until all cells are atheist 1.22S specific gravity. Remove vent caps, if so equipped, and install a thermometer in an electrolyte.
  2. Connect a battery load tester or a battery starter tester, directly to a battery posts: positive to positive: negative to negative.
  3. Turn carbon pile knob to apply a load equal to 50 percent of cold cranking rating of a battery being tested.
  4. Read voltmeter while a load is being applied for 15 seconds. Turn carbon pile knob to off position.
  5. Read thermometer, record temperature, and check temperature and voltage against a chart.
  6. Replace the battery if a minimum voltage is below specification.
  7. If reading is the same or greater than voltage, it shows on chart clean and fully charges. The battery should remain in service.

Load Test Chart

Load Test Chart
Minimum VoltageTemperature
9.670 and above16

The chart above shows readings obtained after 15 sec reading by a battery load tester which has carbon pile.

How To Know Conditions Of A Car Battery Using the Open Circuit Voltage Test

In the open circuit voltage test, if the battery fails the heavy load test, check its state of charge by making a stabilizer open circuit. The voltage test allows at least 10 minutes after the load test for the battery to stabilize then measure and record open circuit voltage.

There are many types of test equipment available for making the open circuit voltage test. In general, a voltmeter and multi-meter are used by connecting its positive lead to the positive post of the battery and its negative lead to the negative post of the battery.

Here are steps to do Open Circuit Voltage Test:

Before you can properly test any battery, it must be at full charge.

You can verify the state of the charge in two ways:

the simplest is done with digital millimeter.

The other test involves the use of a hydrometer.

Using the digital millimeter to verify the state of charge: a fully charged 12 volts battery will read at least 12.6volts (2.1 volts per cell) on the millimeter when connected together.

How To Know Conditions Of A Car Battery
How To Know Conditions Of A Car Battery

Open Circuit Voltage Test Score

Open circuit voltsPercent of charge
11.7 volts or less0%
12.6 or more100%


Philip Nduka

Philip is a graduate of Mechanical engineering and an NDT inspector with vast practical knowledge in other engineering fields, and software.

He loves to write and share information relating to engineering and technology fields, science and environmental issues, and Technical posts. His posts are based on personal ideas, researched knowledge, and discovery, from engineering, science & investment fields, etc.

Please, subscribe to our email list and follow our social media pages for regular and timely updates.

You can follow EngineeringAll social media pages by typing “@ EngineeringAlls” in any social media search form (Facebook, Twitter, Linkedin, Pinterest, Tumblr, etc).

You can submit your article for free review and publication by using the “PUBLISH YOUR ARTICLE” page at the MENU Buttons.

If you love this post please share it with your friends using the social media buttons provided.


Leave a Comment

error: Content is protected !!