How can you test a car battery's state of charge?

To assess a car battery's state of charge accurately, using a hydrometer or a multimeter to measure voltage is a reliable method.

A hydrometer evaluates the specific gravity of the electrolyte solution in the battery cells, which reflects the charge level. When the electrolyte is fully charged, it has a higher specific gravity compared to when the battery is discharged. This method provides a clear indication of the battery's state of charge, making it a popular choice for maintenance checks.

Alternatively, using a multimeter to measure the voltage can also help determine the state of charge. A fully charged car battery should typically read around 12.6 volts or more when the car is off. If the voltage is significantly lower, the battery may be discharged. This method is quick and does not require opening the battery, making it convenient for regular checks.

Visual inspection of battery terminals can identify corrosion or loose connections but does not provide quantitative data about the state of charge. Checking the battery's weight is not a standard method for determining charge levels and does not accurately reflect battery capacity. Measuring the temperature of the battery might indicate issues with performance but does not correlate directly with its charge state. Thus, the most effective methods are those that measure electrolyte properties or voltage directly.