An arrangement for monitoring the current or state of charge (SOC) of an energy system (230) having one or more series-connected strings (S1, S2, . . . Sn) of battery cells (C1, C2, . . . Cn). The battery cells each have respective dissipative devices (D1, D2, . . . Dn) selectively connectable in parallel therewith for balancing cell voltages in the string. The dissipative devices are of predetermined, typically equal, impedance value. The voltage across each cell (Vc1, Vc2, . . . Vcn) may be separately monitored, such that by dividing the monitored voltage across a cell by the impedance value of a dissipative device connected in parallel therewith, the dissipative current is determined. A summation of all of the dissipative currents yields an error value, which error value is then removed from the measured gross current (Ibat) flowing through the combined battery cells and dissipative devices to yield a corrected value of current (Ibatnet). A corrected SOC value (Qnet) is obtainable in a similar manner.