A multi-battery charging system and for reduced fuel consumption and associated emissions for an automotive vehicle. The system starts the vehicle with a start battery in a fuel saving manner, removing electrical torque from alternator shaft, and allows a second (run) battery to provide all or some of the current required by the vehicle loads as fuel savings measure. The start battery is typically recharged after start using the alternator and then switched out of the system in a fully charged state for future vehicle starts. The run battery is typically recharged when its charge level drops below a predetermined level using an on-board battery charging device. The on-board battery charging device is powered from a power line source (e.g., 115 volt or 220 volt ac) external to the vehicle. The system controls the alternator field current with a voltage regulator. The voltage regulator senses the charge level of the two batteries and vehicle operating conditions and provides the proper current into the alternator rotor for maximum fuel savings. The voltage regulator may be a non-microprocessor or a microprocessor controlled device.
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