In June 2006, Tesla reported the Roadster's battery-to-wheel efficiency as 110 Wh/km (17.7 kWh/100 mi) on an unspecified driving cycle—either a constant 60 mph (97 km/h)) or SAE J1634 test—and stated a charging efficiency of 86% for an overall plug-to-wheel efficiency of 128 Wh/km (20.5 kWh/100 mi).