Quick Answer
Specific gravity in lead-acid batteries decreases with age, typically by 0.01 to 0.02 points per year, due to acid stratification and sulfate deposition.
The Effect of Aging on Acid Stratification
The specific gravity in lead-acid batteries decreases with age due to acid stratification and sulfate deposition. Acid stratification occurs when the acid in the battery separates from the water, causing the specific gravity to decrease. As the acid stratifies, it becomes more concentrated near the bottom of the battery, while the water near the top becomes diluted. This can cause a 0.01 to 0.02 point decrease in specific gravity per year.
Sulfate Deposition and Battery Age
Sulfate deposition is another factor that contributes to the decrease in specific gravity with age. Sulfate ions in the battery can precipitate out of solution and form a hard, impermeable layer on the battery plates. This layer can reduce the surface area available for chemical reactions, leading to a decrease in battery performance and a corresponding decrease in specific gravity.
Measuring and Maintaining Specific Gravity
To maintain optimal battery performance, it’s essential to monitor the specific gravity regularly. Using a hydrometer to measure the specific gravity, you can determine if the battery needs to be watered or if the sulfation is severe enough to require a battery conditioner or other treatment. By maintaining the specific gravity within the recommended range, you can extend the life of the battery and ensure reliable performance.
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