A battery electrolyte level monitoring system for a battery having a plurality of cells containing liquid electrolyte, the system comprising: a probe for insertion into one cell of the plurality of cells of the liquid electrolyte battery, being characterised in that the probe includes: a reference electrode, and an electrode array including a plurality of array electrodes arranged in a lengthwise direction of the probe, wherein the reference electrode is capacitively coupled to each array electrode; and a controller electrically coupled to the electrode array, the controller being adapted to: for each array electrode, determine a measured value of a capacitive coupling between the reference electrode and the array electrode, store the measured value for each array electrode, determine an average value of measured values for each array electrode over time, store the average value for each array electrode, compare the average value for each array electrode with a predetermined range corresponding to an acceptable range of the level of the liquid electrolyte within the one cell of the liquid electrolyte battery, and provide a first output if any one of the average values for the array electrodes is above the predetermined range, a second output if all of the average values for the array electrodes are within the predetermined range, and a third output if any one of the average values for the array electrodes is below the predetermined range, the first, second, and third outputs being different from one another. a probe for insertion into one cell of the plurality of cells of the liquid electrolyte battery, being characterised in that the probe includes: a reference electrode, and an electrode array including a plurality of array electrodes arranged in a lengthwise direction of the probe, wherein the reference electrode is capacitively coupled to each array electrode; and a reference electrode, and an electrode array including a plurality of array electrodes arranged in a lengthwise direction of the probe, wherein the reference electrode is capacitively coupled to each array electrode; and a controller electrically coupled to the electrode array, the controller being adapted to: for each array electrode, determine a measured value of a capacitive coupling between the reference electrode and the array electrode, store the measured value for each array electrode, determine an average value of measured values for each array electrode over time, store the average value for each array electrode, compare the average value for each array electrode with a predetermined range corresponding to an acceptable range of the level of the liquid electrolyte within the one cell of the liquid electrolyte battery, and provide a first output if any one of the average values for the array electrodes is above the predetermined range, a second output if all of the average values for the array electrodes are within the predetermined range, and a third output if any one of the average values for the array electrodes is below the predetermined range, the first, second, and third outputs being different from one another. for each array electrode, determine a measured value of a capacitive coupling between the reference electrode and the array electrode, store the measured value for each array electrode, determine an average value of measured values for each array electrode over time, store the average value for each array electrode, compare the average value for each array electrode with a predetermined range corresponding to an acceptable range of the level of the liquid electrolyte within the one cell of the liquid electrolyte battery, and provide a first output if any one of the average values for the array electrodes is above the predetermined range, a second output if all of the average values for the array electrodes are within the predetermined range, and a third output if any one of the average values for the array electrodes is below the predetermined range, the first, second, and third outputs being different from one another.