Abstract: An internal resistance value of a vehicle battery is determined from a measured ripple current. An actual energy content of the vehicle battery is determined from the internal resistance value and a predetermined battery characteristic curve. A temperature value of the vehicle battery is measured and an available amount of energy of the vehicle battery for an emergency pulse is determined based on the actual energy content, an actual discharge current of the vehicle battery and the measured temperature value.

Abstract: A dual battery system includes a starter battery and a battery of the vehicle electric system, a starter and electric consumers that are divided up into start-relevant consumers and consumers of the vehicle electric system. At least one starter switch is interposed between the starter and the starter battery. A first, electronically fully locking switch element is interposed between the starter battery and the start-relevant consumers and a second electrically fully locking switch element is interposed between the battery of the vehicle electric system and the start-relevant consumers. An element is interposed between the starter battery and the battery of the vehicle electric system that prevents the flow of current from the starter battery to the battery of the vehicle electric system and the consumers of the vehicle electric system.