Increasing levels of demand for electrical power for vehicles have prompted a considerable level of research into higher voltage systems. This has resulted in the definition of preliminary standards for 36/42 V systems. The implementation costs for these systems are high and this has led to improvements in 12/14 V power architectures. In particular, alternator power outputs at 14 V have increased and the need for lower emission levels and fuel economy is stimulating a demand for stop-and-go systems. In this type of application, the engine is stopped each time the vehicle comes to a halt, and is restarted when the accelerator is pressed again. The duty cycle that this applies to the battery is quite onerous with many shallow discharge cycles. Flooded lead-acid batteries are unable to meet the requirements and valve-regulated lead-acid (VRLA) batteries are essential to meet the demands applied. The background to stop-and-go battery applications is considered and test results on practical batteries are presented to show that under a simulated duty cycle, good performance can be achieved. There is also a need for a higher level of battery management for stop-and-go systems. A practical approach to battery condition monitoring to assess the state-of-charge and state-of-health of the battery is described. (C) 2004 Elsevier B.V. All rights reserved.