Experimental performances and life cycle estimation of hybrid electric storage systems

The reliability of electrical energy storage systems, related to the various mobile applications, needs to be carefully measured. The Italian research centre ENEA's “Low Environmental Impact Vehicles” Laboratory has started experimental testing activities on storage systems, as illustrated here with reference to acid batteries reliability performances. In this paper, starting from the results of the campaign of laboratory tests, a probabilistic method for describing the distributions of battery lifetime is presented. The approach is based upon the Rakhmatov and Virudhula battery model. In the final part of the paper, numerical tests show that the battery expected lifetime can be well described by models, such as the Inverse Weibull or the Lognormal, with decreasing hazard rate for large mission times, a fact which has been sometimes observed in literature as a paradox. Some considerations with respect to parameter estimation of the reliability models close the paper.