Within the framework of the European project bipolar lead-acid power source (BILAPS), a new production route is being developed for the bipolar lead-acid battery. The performance targets are 500 W kg(-1), 30 Wh kg(-1) and 100 000 power-assist life cycles (PALCs). The operation voltage of the battery can be, according to the requirements, 12, 36 V or any other voltage. Tests with recently developed 4 and 12 V prototypes, each of 30Ah capacity have demonstrated that the PALC can be operated using 10C discharge and 9C charge peaks. The tests show no overvoltage or undervoltage problems during three successive test periods of 16 h with 8 h rest in between. The temperature stabilizes during these tests at 40-45 degrees C using a thermal-management system. The bipolar lead acid battery is operated at an initial 50% state-of-charge. During the tests, the individual cell voltages display only very small differences. Tests are now in progress to improve further the battery-management system, which has been developed at the cell level, during the period no PALCs are run in order to improve the hybrid behaviour of the battery. The successful tests show the feasibility of operating the bipolar lead-acid battery in a hybrid mode. The costs of the system are estimated to be much lower than those for nickel-metal-hydride or Li-ion based high-power systems. An additional advantage of the lead-acid system is that recycling of lead-acid batteries is well established. (c) 2004 Elsevier B.V. All rights reserved.