Reference voltage for an accumulator

The invention discloses an accumulator, with - a plurality of modules, each having at least one battery cell; - a plurality of module monitoring devices, each monitoring at least one module; - a Akkumulatoruberwachungseinrichtung, which is adapted to monitor the accumulator; - a first reference voltage source, which is adapted to hold a reference voltage for a first period within a tolerance range; and - a plurality of second reference voltage sources which are adapted to hold a reference voltage for a second period within a tolerance range, wherein the first period is longer than the second time period; - wherein the first reference voltage source is arranged in the Akkumulatoruberwachungseinrichtung or in a module monitoring equipment; and - wherein a second reference voltage source is arranged in those monitoring device module in which no first reference voltage source is arranged; - further comprising a calibration device which is configured to determine the reference voltage of the second reference voltage source based on the reference voltage of the first reference voltage source and / or change.