High Power Lead-Acid Battery for Heavy-Duty HEV, On the Road and Laboratory Performance and Reliability

When the first hybrid vehicles were commercialized in the early '90, traction lead-acid batteries were used as on board storage system, and their limits in this application were soon complained from users and recognized by manufacturers. Therefore the battery industry has developed specific high-power lead-acid batteries, which constitute an industrialized and economic alternative to the alkaline batteries (Ni-Cd, Ni-MeH). Under the direction and funding support of the Commission of the European Community, the R&D Organization EUCAR (European Council for Automotive Research, a collaborative partnership of most European car manufacturers), has been conducting an autonomous characterization activity of these high-power systems using agreed test procedures, through bench tests carried out by different independent laboratories throughout Europe. In this framework, ENEA acted as independent testing institute and tested, among others, three high power lead-acid batteries of various technologies (flat plate electrodes and spiral wound) for EV and HEV applications. In addition, different battery sizes and operating conditions have been tested at ENEA in a separate collaboration with ALTRA-IRISBUS with life-cycle tests performed under very heavy conditions. ALTRA-IRISBUS has introduced these batteries on its vehicles (nowadays one of the greatest fleets of this type in Europe, with about one hundred vehicles on the road) with the purpose to improve performance and reliability. This article illustrates therefore the principal results of these bench and on road experiences, the advancements accomplished in terms of performance, life and reliability, with special emphasis on the reduction of the internal resistance and the variation of peak power and cycle life, and underlines the principal improvements needed to guarantee full reliability of this automotive storage system.