Another drawback, for the moment anyway, is the cost. The initial installation is more expensive than that of a conventional diesel auxiliary. For an ST 37, the electric motor itself costs about $10,000. The entire system--which includes 4D batteries, cables, meters, a charger, a throttle, a 3-kilowatt inverter, and a 6-kilowatt genset--costs about $35,000. Of that, the genset accounts for $11,000. An ST 74 motor, recommended to replace diesels up to 48 horsepower, costs $12,000. That entire system, including the same extras but with 8D batteries, a 6-kilowatt inverter, and a 9-kilowatt genset, costs just over $40,000.