Battery voltage test

A battery voltage test is a quick and relatively accurate indication of the state of charge in an open circuit. A digital multimeter is used for voltage measurement. The test is applied to sealed accumulators without maintenance and a built-in hydrometer, as a substitute for testing the electrolyte density.

Depending on the degree of charge, the battery voltage changes. The battery temperature should be between 15°C and 38°C. Before measuring, the battery should stabilize for at least 10 minutes, without load. On vehicles, with high discharges (control units, clocks, and accessories that always consume a small amount of current) it may be necessary to disconnect the minus terminal from the battery. If the battery has recently been charged, remove the surface charge by turning on the headlights for three to five minutes.

The relationship between open circuit voltage and specific gravity/ state of charge of a battery

When the voltage stabilizes, measure the battery voltage with a digital voltmeter. A fully charged battery should have a voltage of 12.6 V or more. A measured voltage of 12.4 V indicates a charge of about 75%, and 12.0 V indicates that the battery is empty.

If the test shows that the charge is below 75%, charge the battery and perform a capacitance test to determine its condition.

To perform a battery voltage test, follow these steps:

Preparation for measurement

Check the battery temperature. If recently charged, remove the surface charge by turning on the headlights for three to five minutes. Remove the minus terminal and let the battery voltage stabilize for 10 minutes.

Voltage measurement

Use a digital multimeter to measure the battery voltage between its poles.

Measurement analysis

Based on the measured voltage, estimate the charge level of the battery from the graph. If the charge is below 75%, charge the battery, remove the surface charge and perform the charge test again.