Lead acid batteries offer important advantages in respect of unit cost and ease of recycling. They also have good power and low temperature performance. However, for hybrid electric vehicle (HEV) duty with their extreme rates and continuous PSoC operation, improvements are required to significantly extend service life. The Reliable Highly Optimised Lead Acid Battery (RHOLAB) project is taking a radical approach to the design of a lead acid HEV battery pack to address this issue, taking a systems approach to produce a complete pack that is attractive to vehicle manufacturers. This paper describes the project at an intermediate stage where some testing has been completed and the construction of the complete pack system is well under way. (C) 2003 Elsevier Science B.V. All rights reserved.