A discharge control system of a vehicle includes a traction power inverter module (TPIM) configured to convert a first direct current (DC) voltage output by a first battery to alternating current (AC) power and apply the AC power to an electric motor. An accessory power module (APM) is configured to convert the first DC voltage into a second DC voltage of a second battery. A voltage calculation module is configured to, when the first DC voltage is less than an operation threshold voltage of the APM, determine the second DC voltage based on a function of the first DC voltage and the operation threshold voltage. A diagnostic module is configured to indicate whether a discharge fault is present. A discharge control module is configured to, when the discharge fault is present, based the first DC voltage and the second DC voltage, selectively control operation of the TPIM and the APM.