Is there a correlation between specific gravity and battery amp-hour?

Understanding Specific Gravity

Specific gravity is a measure of the density of a battery’s electrolyte compared to the density of water. It is commonly used to monitor the state of charge of lead-acid batteries. A fully charged battery typically has a specific gravity of 1.260 to 1.300, while a fully discharged battery has a specific gravity of around 1.150.

Measuring and Interpreting Specific Gravity

To measure specific gravity, you will need a hydrometer or a specific gravity test kit. When reading the specific gravity, it’s essential to note the temperature of the electrolyte, as temperature affects the specific gravity. A change in specific gravity indicates a change in the battery’s state of charge. For example, if the specific gravity reads 1.220, it means the battery is 75% charged, assuming a fully charged specific gravity of 1.300.

Calculating Amp-Hour Capacity

To calculate the amp-hour capacity of a battery based on specific gravity, you can use the following formula: Amp-hour capacity = (Specific gravity x 5) + 10. For example, if a 100Ah battery has a specific gravity of 1.220, its amp-hour capacity would be 100 x (1.220 x 5) = 610Ah. However, this calculation should not be used for precise calculations, as it is an estimate based on a simplified formula.