communicate status control and data by interface ports the use of the interface ports is known to those skilled in the art the digital representation of v1 v2 v3 are presented to the microprocessor as v1 39 29 v1 39 30 and v3 39 31 respectively the program in the microprocessor executes the functions described next the sum of vcell1 dv is subtracted from vcell2 resulting in vd1 the sum of vcell1 dv is subtracted from vcell3 resulting in vd2 the sum of vcell2 dv is subtracted from vcell1 resulting in vd3 the sum of vcell2 dv is subtracted from vcell3 resulting in vd4 the sum of vcell3 dv is subtracted from vcell1 resulting in vd5 the sum of vcell3 dv is subtracted from vcell2 resulting in vd6 if the values in vd1 vd6 are less than 0 then led2 17 is illuminated which indicates all cells are operating appropriately else led1 16 is illuminated which indicates a defective cell has been detected led1 16 is illuminated by setting output port p1 32 on the microprocessor to a low value near 0 volts and simultaneously setting microprocessor port output port p2 33 to a high value near vcc current will flow from p2 33 through led1 16 and resistor 34 causing led1 16 to illuminate led2 17 is illuminated by setting output port p1 32 on the microprocessor to a high value near vcc and simultaneously setting microprocessor port p2 33 to a low value near 0 volts current will flow from output port p1 32 through led2 17 and resistor 34 causing led2 17 to illuminate led1 and led2 are shown as separate elements but are also available as a single combination device additional components in fig4 are required for complete disclosure the most negative.