VRLA battery capacity measurement and discharge reserve time prediction

This paper addresses the issue of correlating the battery discharge voltage with the battery reserve capacity. The approach uses base discharge characteristics obtained under nominal operating conditions as a reference for capacity measurement during battery lifetime. This gives a reasonable prediction of reserved capacity over both the normal and some extreme operating conditions of temperature and discharge rate. A simple, effective and economical solution has been developed for battery capacity measurement and reserve time prediction. The algorithm is based on a nominal discharge characteristic table and utilises the online battery parameters of discharge rate, voltage and temperature. This yields a robust approach that bounds the measurement uncertainty to within a given tolerance band (-4% and +8%). Tests have been performed on different single cells, groups of cells, monoblocs and strings of cells of the same plate type. The temperature was varied from moderately cold to extremely hot and the discharge rate was varied over the normal operating range