Process for determining the state of charge and the peak current loadability of batteries

In a process for determining the state of charge and the peak current loadability of batteries in the currentless pauses before and after a loading phase the no-load voltages U01 and U02 are measured. From them, with allowance for battery-specific parameters, especially the time curve of the no-load voltage, the true battery rest voltages U001 and U002 are computed. During the loading phase the converted current quantity q is measured and from the relationship U002-U001=C1xq/Q0 the acid capacity Q0 of the battery is found. The relative state of charge SOC1 is determined from a curve of the rest voltage U00 linearized by the formula SOC1=U002/C1-C2 as a function of the state of charge of the battery from which the absolute state of charge is calculated as SOC1xQ0. From the internal resistance R1, a preassigned temperature and the last determined state of charge, a rest voltage is predicted for a later time from which, with the current necessary for starting the engine known, a pronouncement can be derived concerning the starting capacity of the battery.