Quick Answer
Specific gravity of a battery decreases as it ages due to the loss of sulfuric acid through internal reactions, which changes the chemical makeup of the electrolyte, affecting the overall performance and lifespan of the battery.
Understanding Specific Gravity
Specific gravity is a measure of the density of a battery’s electrolyte compared to that of water. It is an essential parameter for evaluating a battery’s state of charge and health. For a fully charged battery, the specific gravity should range from 1.265 to 1.315 for most deep cycle lead-acid batteries.
Measuring Specific Gravity
To measure specific gravity, you can use a hydrometer, which is a device that measures the density of a liquid. When taking a specific gravity reading, make sure the battery has been at rest for a few hours and the temperature is between 77°F and 86°F (25°C and 30°C). This ensures accurate readings. Always take multiple readings to confirm consistency.
What to Expect as Batteries Age
As batteries age, their specific gravity will decrease due to the natural degradation of the electrolyte. A typical lead-acid battery will lose around 3-5 points of specific gravity per year, depending on usage and environmental factors. For example, a fully charged battery with a specific gravity of 1.300 at the start of the year may drop to 1.250 by the end of the year. This decrease in specific gravity can indicate a decrease in battery capacity and overall performance.
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