Is there a significant difference between specific gravity and rest state?

Understanding Specific Gravity

Specific gravity is a critical measure of a battery’s health, particularly in lead-acid batteries. It represents the ratio of the density of the electrolyte solution to the density of pure water. A specific gravity reading below 1.260 indicates an undercharged battery, while a reading above 1.300 suggests overcharging. To accurately measure specific gravity, a hydrometer is used, which should be calibrated annually.

Rest State Readings

Rest state readings, on the other hand, assess a battery’s overall health by measuring its internal resistance, voltage, and capacity. A rest state reading can indicate a battery’s ability to hold a charge and supply power when needed. For a typical 12V battery, a rest state reading of 12.7V or higher is generally considered good. Internal resistance below 20 milliohms is also a good indicator of a healthy battery. However, a battery with high internal resistance can lead to reduced capacity and lifespan.