The SG-Electrode is designed to measure the specific gravity of the electrolyte, and therefore state of charge, in a flooded lead acid battery.
Measuring the SG of battery electrolyte effectively involves determining the amount of water and sulfuric acid in the mixture. Water is important because the average concentration of water in the battery cells is proportional to the degree of charge of the battery. This is best understood by considering the overall reaction occurring in a lead-acid battery, which may be written as:
As the battery discharges, sulfuric acid (H2SO4) is consumed and water (H2O) is produced. This process reverses when charging occurs. The weight percent water in battery acid may vary from about 60% (fully charged) to 95% (discharged state) and the measured value relative to this range can be used as an indication of the fraction of available energy stored in the battery (i.e. state-of-charge). Because of the widespread use of hydrometers to determine battery acid concentration it has become common practice to use specific gravity as a measure of battery state-of-charge. In recognition of this, the microprocessor inside the display unit provided with the SG-Electrode is programmed to convert water concentration into SG units, standardized to 20 degrees C. The system has provision for calibration using standard solutions of sulfuric acid. Applications include solar and wind power battery storage systems, remote power backup batteries, submarine battery monitoring and off-grid power supplies.
SG-Electrode Lead Acid Battery State-of-Charge Sensor