Vehicle battery system providing battery back-up and opportunity charging

摘要

A battery system for a vehicle includes a main battery for energizing the vehicle SLI circuits and an auxiliary battery for energizing the vehicle EHC system, the battery system providing back-up of the auxiliary battery by the main battery under certain conditions and back-up of the main battery by the auxiliary battery under certain other conditions, and the battery system providing opportunity charging of the auxiliary battery once the vehicle engine is running whereby the auxiliary battery shares the charging current with the main battery with the auxiliary battery being gradually connected to the source of charging current for the main battery by increasing the duty cycle of the drive circuit that connects the auxiliary battery to the source of charging current while monitoring the state of charge of the main battery and decreasing the duty cycle of the drive circuit to protect the main battery state of charge. In other embodiments, separate sources of charging current are provided for the auxiliary battery.