Abstract: A kit for converting a standard hybrid vehicle into a plug-in hybrid vehicle (PHEV) is described. The kit includes at least one battery configured to match the voltage of an original hybrid battery; connection hardware, wherein the connection hardware is configured to electrically connect the at least one battery to an off-vehicle power source; and tangible computer readable memory media storing battery management software, wherein when executed in a processor in a vehicle, the battery management software is configured to provide information relating to battery performance to an engine control unit, wherein the at least one battery is further configured to maintain charge balance between each of the cells of the at least one battery.