In September 2000, a project reliable, highly optimized lead-acid battery (RHOLAB) started under the UK Foresight Vehicle Programme with the objective of developing an optimized lead-acid battery solution for hybrid electric vehicles. The work is based on a novel, individual, spirally-wound valve-regulated lead-acid 2 V cell optimized for HEV use and low variability. This cell is being used as a building block for the development of a complete battery pack that is managed at the cell level. Following bench testing, this battery pack is to be thoroughly evaluated by substituting it for the Ni-MH pack in a Honda Insight. The RHOLAB cell is based on the 8 Ah Hawker Cyclon cell which has been modified to have current take-off at both ends-the dual-tab design. In addition, a variant has been produced with modified cell chemistry to help deal with problems that can occur when these valve-regulated lead-acid battery (VRLA) cells operate in a partial-state-of-charge condition. The cells have been cycled to a specially formulated test cycle based on real vehicle data derived from testing the Honda Insight on the various test tracks at the Millbrook Proving Grounds in the UK. These cycling tests have shown that the lead-acid pack can be successfully cycled when subjected to the high current demands from the vehicle, which have been measured at up to 15 C on discharge and 8 C during regenerative recharging, and cycle life is looking very promising under this arduous test regime. Concurrent with this work, battery development has been taking place. It was decided early on to develop the 144 V battery as four 36 V modules. Data collection and control has been built-in and special steps taken to minimize the problems of interconnect in this complex system. Development of the battery modules is now at an advanced stage. The project plan then allows for extensive testing of the vehicle with its lead-acid battery at Millbrook so it can be compared with the benchmark tests which have already been carried out on the vehicle with its Ni-MH batteries. (C) 2004 Elsevier B.V. All rights reserved.