Low-temperature preheating of batteries is fundamental to ensure that electric vehicles exhibit excellent performance in all-climate conditions. Direct current for discharge is presented to rapidly preheat batteries due to its simple implementation and high heat generation compared to alternating current. Experimental results reveal that the heating time is significantly reduced while capacity degradation is dramatically increased, with the decreasing discharge heating voltage. A simple fade model to capture battery capacity loss is proposed and accurately demonstrated under direct-current discharge heating. Pareto front for dual crucial yet conflicting objectives, heating time and capacity loss, is obtained using the multi-objective genetic algorithm and the effect of weighting coefficient on heating performance is discussed, thus proposing an optimal internal-heating strategy. The battery is rapidly heated from −30 °C to 2.1 °C within 103 s and the capacity loss is only 1.4% after 500 repeatedly heating, implying substantially no lifetime deterioration. At 0.8 state-of-charge, the heated battery can offer 8.7/32.7 times the discharge/charge power and 62.46 times the discharge energy of the unheated battery, indicating a significant performance boost. The proposed optimal heating method, thanks to short heating time and no substantial lifetime reduction, yields great potential to rapidly boost battery performance in extremely cold conditions.