The invention relates to a method and arrangement for determining a power supply state variable, particularly of the maintenance state of a battery or rechargeable battery, in an active medical implant, wherein the power supply is subjected to a predetermined load, and the output voltage thereof is detected multiple times during at least one time segment of the load phase, and the measurement values are subjected to a comparison to a respective comparison value, or the chronological curve of the voltage obtained from the measurement values is subjected to a comparison to at least one comparison curve, wherein the comparison result is considered characteristic for the state variable.