End-user experience of VRLA batteries

Field experience from the use of various makes and types of VRLA batteries, commonly used for telecom and power distribution applications, is analyzed. More than 1000 installations, of various system voltages and cell capacities, comprising about 35000 cells, are reviewed and statistics from operation as well as failure rate analysis are presented. Input data cover up to six years of use of so called "10 year batteries". Various component reliability data, e.g. MTBF for makes and system voltages, suitable for system reliability and economic analysis, are presented and discussed. The results show significantly shorter battery life than predicted by the manufacturers' "Eurobat guide". The failure frequency for batteries correlates well, as was to be expected, with system voltage. This emphasizes the importance of distinguishing between cells and batteries when stating system life. It is concluded that there is a need for a new, concise, application-oriented life concept for batteries to be established. One way to begin doing so would be to instigate an international study of the subject, with a broad international participation to get it well accepted as the base for future work towards better reliability and economy of battery supported stationary installations.