A battery control system configured to control operation of a battery system for an electric or hybrid electric vehicle, the battery control system comprising: - a first string control unit communicatively coupled to a first serial bus, wherein the first string control unit is configured to: - control operation of a first battery string comprising a first one or more battery modules connected in series; and - output a first serial communication signal to the first serial bus, wherein the first serial communication signal comprises a first frequency to indicate that the first string control unit is a master string control unit when a first fault is not detected in the first battery string; and - a second string control unit communicatively coupled to the first serial bus and a second serial bus, wherein the second string control unit is configured to; - control operation of a second battery string comprising a second one or more battery modules connected in series, wherein the second battery string is coupled in series with the first battery string; - receive the first serial communication signal from the first serial bus; - determine that the second string control unit is a first subordinate string control unit when the first serial communication signal comprises the first frequency; and - output a second serial communication signal to the second serial bus, wherein the second serial communication signal comprises a second frequency to indicate that the second string control unit is the first subordinate string control unit when a second fault is not detected in the second battery string. - a first string control unit communicatively coupled to a first serial bus, wherein the first string control unit is configured to: - control operation of a first battery string comprising a first one or more battery modules connected in series; and - output a first serial communication signal to the first serial bus, wherein the first serial communication signal comprises a first frequency to indicate that the first string control unit is a master string control unit when a first fault is not detected in the first battery string; and - control operation of a first battery string comprising a first one or more battery modules connected in series; and - output a first serial communication signal to the first serial bus, wherein the first serial communication signal comprises a first frequency to indicate that the first string control unit is a master string control unit when a first fault is not detected in the first battery string; and - a second string control unit communicatively coupled to the first serial bus and a second serial bus, wherein the second string control unit is configured to; - control operation of a second battery string comprising a second one or more battery modules connected in series, wherein the second battery string is coupled in series with the first battery string; - receive the first serial communication signal from the first serial bus; - determine that the second string control unit is a first subordinate string control unit when the first serial communication signal comprises the first frequency; and - output a second serial communication signal to the second serial bus, wherein the second serial communication signal comprises a second frequency to indicate that the second string control unit is the first subordinate string control unit when a second fault is not detected in the second battery string. - control operation of a second battery string comprising a second one or more battery modules connected in series, wherein the second battery string is coupled in series with the first battery string; - receive the first serial communication signal from the first serial bus; - determine that the second string control unit is a first subordinate string control unit when the first serial communication signal comprises the first frequency; and - output a second serial communication signal to the second serial bus, wherein the second serial communication signal comprises a second frequency to indicate that the second string control unit is the first subordinate string control unit when a second fault is not detected in the second battery string.