What is the procedure for testing a battery's state of charge?

To determine a battery's state of charge, using a multimeter to measure the voltage is a straightforward and effective method. A multimeter can give you a direct reading of the battery's voltage, which correlates with its state of charge. A fully charged lead-acid battery, for example, should read around 12.6 volts or higher when it’s not under load. As the voltage decreases, so does the state of charge. This method provides immediate results and requires minimal setup and equipment.

The other methods, while relevant to battery maintenance, do not directly assess the state of charge as effectively or straightforwardly. Using a hydrometer measures the specific gravity of the electrolyte in each cell but is typically more applicable to flooded lead-acid batteries and requires some knowledge and experience to interpret the readings. Inspecting the physical condition of the battery terminals can help identify surface issues or corroded connections but does not provide information about the battery's charge level. Performing a load test using a dedicated battery tester assesses the battery's ability to deliver sufficient current under load, which can indicate overall battery health, but again, it isn't a direct measurement of the state of charge.