Density and viscosity measurements in lead acid batteries by QCM sensor

In automotive applications, submarines and remote communication systems it is necessary to know the state of charge (SOC) of the batteries in order to manage them efficiently. Due to the acid concentration dependence of SOC, traditionally, density measurements are done in order to estimate it. But other parameters like electrolyte viscosity have highest changes with SOC than density. In this paper, a QCM (Quartz Crystal Microbalance) oscillator sensor for monitoring density and viscosity changes in lead-acid batteries is presented. The frequency shift is monitoring in solutions with H₂SO₄ concentration in the battery electrolyte range and the sensitivity and resolution of the sensor are determining for the application. Then, successful experiments are carried out by placing the quartz crystal inside the battery cell.