The micro hybrid system, also known as the engine stop start system, has recently gained prominence world over due to its considerable fuel saving potential and relatively low costs. In spite of being a relatively non-complex function, the stop start system works hand-in-hand with a wide range of vehicle systems and components, specially the starting system and the battery. Frequent idle stop periods during city driving conditions can result in excessive battery discharge and gradually lead to loss of engine restartability. Increased number of charging and discharging cycles tend to reduce the life of the battery significantly. Hence it is very essential that the micro hybrid vehicles have a system in place that monitors and maintains the battery status within its operating limits. This paper describes a battery management system that is designed to ensure engine restartability, maintain system voltage and improve battery life while allowing a significant number of stop-start cycles to ensure considerable fuel-saving. The micro hybrid battery management system architecture, components and the functional behavior are presented here in detail along with vehicle level test measurements.