The development of novel electrical systems for low emission vehicles demands batteries with specific cycling performance, especially under partial state of charge (PSOC) conditions. Moreover, according to the powertrain design, battery high power capability is demanded or this function can be assumed by a supercapacitor or a flywheel. This paper deals with the development of AGM and gel valve-regulated lead-acid batteries for advanced automotive applications. AGM VRLA battery development was based on previous work for short autonomy high power UPS applications and on active material formulations with specific additives to improve battery life under high rate partial state of charge cycling conditions. The 18 Ah batteries showed excellent high rate capability (9 kW 10 s discharge peaks and 4 kW 5 s regenerative charge acceptance at 60% state of charge) and 110,000 power assist microcycles at 60% SOC and 2.5% DOD were fulfilled. Moreover, as preliminary work in the development of a cost-effective and reliable gel battery to be used in combination of a supercapacitor in a 42 V mild-hybrid powertrain, VRLA batteries with conventional gel formulations have been tested according to novel automotive cycling profiles, mainly moderate cycling under partial state of charge conditions and simulating load management in a stop and start working profile. (c) 2004 Elsevier B.V. All rights reserved.