The invention relates to devices and/or methods for determining the availability of electrical energy in two-energy accumulator vehicle electric systems, in which both energy accumulators, particularly batteries, can be connected to one another via a D.C. converter. The required electric energy is generated by means of a generator that is driven by a vehicle engine. The customary consumers are connected to a first consumer battery circuit (10, 24). Additional consumer, for example, high-current consumers, particularly the starter, are connected to the second battery circuit (11, 29). A control device, for example, a controller that is equipped with a microprocessor determines the availability of the electric energy and occurring faults while evaluating.