There are many ways to test a battery’s condition and usually one type of battery test will not conclude a faulty battery.
- Electrolyte specific gravity test.
- Load testing.
- Internal resistance tests. (Smart battery testers)
- Voltage test.
Electrolyte Specific gravity test.
When using this test method, you need to access the batteries acid, on maintenance free batteries you cannot access the cells so this type of testing is usually not conducted anymore, added to that is this test is messy, leaving drops of acid is not a good thing.
How it works
A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water.
The test is measuring the charge of the battery and not the integrity of the battery. the table at the bottom of this page demonstrates the specific gravity and charge level of a battery.
Load testing a battery is placing a load on the battery with either a carbon pile or a heating up a large element, which will act like a starter motor, drawing current from the battery, while using this test you are testing the batteries efficiency to produce voltage, a good charged battery should be able to produce high current with a loaded voltage of around 10 volts, as the battery ages or if the batteries charge is low, the load testers indicator will drop. with a poor battery usually after the test has been conducted the vehicle will not start confirming that the battery is in poor condition.
the load tester is also a great way to remove any static over charging. which will aid in other tests for accurate testing.
Internal resistance tests (smart battery testers)
As most batteries are now maintenance free conducting a specific gravity test on the acid cannot be done, clever people have come up with a battery tester that tests the internal resistance of the battery and will produce a CCA rating of the battery, this is done by connecting the tester on the + Positive and – Negative terminals, then you select the CCA rating of the battery then the battery conducts the test and comes back with a CCA rating on the battery which will show the output CCA rating of the battery.
Example if a battery has a CCA ratting of 450 CCA and the test comes back with 220 CCA rating chances are that the batteries life is almost over. Having experience with this type of test a battery that comes back with a 220 CCA rating will usually fail with in a short period and we recommend a battery change on that day rather than waiting a few months to find that one morning you cannot start the vehicle.
We use a Bosch battery internal tester when testing a battery during a service showing a quick and accurate way to inform the client of the vehicles battery condition, if the battery test come back with a low reading we will then test the battery with other methods to confirm the battery condition.
A voltage test is a simple test and can be tested with simple testing equipment a voltmeter placed on the + positive and – negative terminals will show a voltage reading. below is a table for the battery charge condition using a voltmeter.
Battery Voltage Explained
The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery by:
|Open Circuit Voltage (12 V)||Approximate charge||Relative acid density|
|12.60 V||100%||1.265 g/cm3|
|12.45 V||75%||1.225 g/cm3|
|12.24 V||50%||1.190 g/cm3|
|12.06 V||25%||1.155 g/cm3|
|11.89 V||0%||1.120 g/cm3|