Temperature compensation of float voltage-the special situation of VRLA batteries

Float charging of valve-regulated lead-acid batteries is a complex combination of various electrochemical reactions: internal-oxygen cycle, hydrogen evolution at the negative electrode, corrosion of the positive grid, and also discharge reactions of positive and negative electrodes that can occur in unfavourable circumstances. To derive general rules for temperature compensation, a mathematical model was applied, that describes the effects of float conditions and kinetic cell parameters on electrode potentials and electrode-reaction rates. The required kinetic parameters were determined in meticulous measurements with two quite different types of test cells, one with high, the other one with low oxygen reduction efficiency. The model assumptions were verified by experimental results within reachable accuracy. Optimum float voltage is determined by certain polarisation of positive and negative electrodes. Effects of float voltage and temperature on electrode polarisation were simulated in the range between 0 and 50°C