How to Determine the Capacity of Flooded Lead-Acid Batteries?

Calculating Battery Capacity

To determine the capacity of flooded lead-acid batteries, check the ampere-hour (Ah) rating on the battery. This rating is usually marked on the battery itself or in the manufacturer’s documentation. The Ah rating is the product of the battery’s voltage and capacity.

For example, a 12V, 200Ah battery has a capacity of 200Ah at the 20-hour rate. The 20-hour rate is a standard method used to measure battery capacity, where the battery is discharged at a rate of 0.05A (1/20th of the capacity) and the time taken to reach 1.75V per cell is measured.

Checking Battery State and Condition

Before checking the battery capacity, verify the battery’s state of charge and condition. A fully charged battery with no signs of physical damage or corrosion will provide the most accurate capacity readings. Use a hydrometer to check the battery’s electrolyte levels and specific gravity, which should be within the manufacturer’s specified range.

Interpreting Battery Capacity Readings

Interpret the battery’s capacity readings carefully, taking into account any deviations from the manufacturer’s specifications. Consult the manufacturer’s documentation for guidance on how to interpret the readings and what to expect from the battery’s performance under different conditions. If the battery’s capacity readings are significantly lower than expected, it may be necessary to retest the battery or replace it with a new one.