A battery and supercapacitor system of a vehicle includes a lithium ion battery (LIB) having first and second electrodes, and a supercapacitor having third and fourth electrodes. A first reference electrode is disposed between the first and second electrodes and is configured to measure a first potential at a location between the first and second electrodes. A second reference electrode is disposed between the third and fourth electrodes and is configured to measure a second potential at a location between the third and fourth electrodes. The first electrode may be connected to the third electrode, and the second electrode may be connected to the fourth electrode. The first and second reference electrodes may not be connected to any of the first, second, third, or fourth electrodes.