Everyone knows that car batteries can struggle in cold weather and are more likely to fail in the winter months. Battery experts GS Yuasa have issued some advice to garages on spotting battery issues and explained some of the common terms used to describe battery health.

Ian Newham, Training Manager at GS Yuasa says that the State of Charge (SOC) of an automotive battery is expressed as a Voltage (OCV) and is the force used to push the starting current known as Cold Cranking Amps (CCA) through the starter circuit to the starter motor. A fully charged battery is can achieve approximately 100% of its starting capacity, but if a battery has a low OCV its ability to force CCA through the starter circuit is reduced resulting in a possible non-start even though the battery may have a good State of Health (SOH).

Each time a battery is discharged and recharged, known as a cycle, a small amount of the plate material that chemically reacts with the sulphuric acid in electrolyte solution to produce electricity is permanently lost. Over time, and dependent on factors such as operating temperature, operating state of charge and duty cycle this natural usage of the plate material will eventually result in a slow but steady reduction in the SOH of the battery and its ability to produce the CCA required by the starter motor.

Ian says it is easy to confuse SOC with SOH and make incorrect diagnostic assumptions when battery failure occurs. If the battery SOC is low but it has a good SOH, engine starting capability can be recovered by recharging the battery and restoring its ability to push the available CCA through the starter circuit. However if the SOC is high but the SOH is low as the battery plate material has deteriorated over time a non-start situation is likely to occur even though the battery is fully charged.

The SOH of a battery and its ability to supply high levels of CCA becomes even more important during the cold winter months. This is because the ability of a battery to supply the maximum available CCA is reduced by approximately 30% at 0°C. However the CCA requirements of the starter circuit increase in order to overcome conditions such as increased engine oil viscosity and reduced engine component tolerances.
It is therefore possible to have a battery that is fully charged with a good OCV that will still not be able to start the engine as the SOH and its ability to deliver high levels of CCA has reached a level that is unable to support the requirements of the starter circuit.

Yuasa Batteries are available from stockists nationwide and distributed in Ireland by Somora.