Is Voltage the only parameter of 12v battery health?

SOC vs SOH for Battery Testing

We all have one time or the other called a local auto mechanic and asked for checking our car battery. In many cases, they come with a voltmeter, check the voltage and give a judgement. If the voltage is low then the battery needs to be replaced. Here comes the difference between State of Charge and State of Health.

However, there are a few more parameters that need to be checked so that you can be sure that the battery is ok, can be saved or needs to be discarded. Let’s look at them one by one.

CCA in Battery Testing

CCA stands for Cold Cranking Amps. I will not go into the pure technical definition but in layman terms, it is the value that defines how much energy the battery can shoot out when you turn that key to start your car or bike. A standard Maruti Suzuki Baleno uses a 12v, 35Ah, 220 CCA battery. Although in many countries it is mandatory for battery manufacturers to declare the CCA, in India it is not the case. So you need to use the Ah (Battery Capacity) to determine the CCA. Use the below conversion chart if required. So if the CCA falls below the declared value by over 40%, it means you are heading towards a battery failure. Using a battery tester that checks this is useful. In the above example if the CCA is 100 on measurement, then you need to take corrective steps.

CCA and DIN useful for Battery Testing

IR or Internal Resistance in Battery Testing

IR decides how well the battery can accept, retain and release the charge. A high means less battery capacity to hold the charge and hence faster discharge. Typically the value should be close to 5 and as it increases to 7 and above we are in trouble land. Use a Battery Tester than can help you get that value.

Internal Resistance in Battery Testing


Did you know that a 12v battery is considered fully charged at 12.72 volts and discharged at 12 volts? However, it does not mean that at 11.9 volts the battery is gone. It just means we are in need of help. As the battery voltage drops below 12 volts, the battery starts to desulphate. This desulfation is what affects the IR. So it is best to keep the battery charged and this can easily be done by charging the battery every 2 months for a few hours using a reliable. This will help increase battery life by 2 to 3 times.

Voltage check in Battery Testing

Other Factors

There are a couple of things that you need to keep in mind which affect the battery condition. It is the alternator and the starter. In case, the alternator is not able to provide the required charge with the battery will discharge fast despite it being in good condition. On the other hand a worn out starter will put unnecessary pressure on the battery and drain the battery without actually starting the vehicle. The Testers today can actually check these for you. So rely on modern-day Battery Tester like the Foxwell BT780, 705 or the Konnweei KW600.

Always remember that battery testing should be tested only in cold condition, meaning not just after stopping the car or just after charging. Give it 15 – 30 minutes before you go ahead with the testing.

Image Courtesy – Varta