Abstract: An electric motor drive retrofit system (EMDRS) comprises a power system, an energy storage system (ESS), a cooling system, a vehicle control unit (VCU), and a user interface device (UID). A non-hybrid combustion engine drive vehicle with tight space constraints is retrofittable with the EMDRS to provide hybrid drive functionality. EMDRS includes a motor generator unit (MGU) coupled to a motor control unit that transfers charge between MGU and ESS. During retrofit, the MGU is coupled between a transmission and an internal combustion engine (ICE) of the vehicle without extending a powertrain length by more than five inches. VCU does not interfere with any pre-existing vehicle electronics. The VCU controls the EMDRS to add torque (discharging ESS) or to remove torque (charging the ESS) based on a selected operating mode and vehicle sensor information (for example, brake and throttle pressure). Operating modes are selected by driver via the UID.