A vehicle includes an engine, fraction motor, final drive assembly, battery pack, and a supercapacitor module electrically connected to the battery pack. The vehicle also has first and second clutches and a controller. The clutches have opposite apply states. The first clutch connects an engine driveshaft to the motor to establish a neutral-charging mode. The second clutch connects an output shaft of the motor to the final drive assembly to establish a drive mode. The controller selects between the drive and neutral-charging modes in response to input signals. The drive mode uses energy from the supercapacitor module and battery pack to power the traction motor. The neutral-charging mode uses output torque from the engine to charge the supercapacitor module and battery pack. The clutches may be pneumatically-actuated, and the vehicle may be characterized by an absence of planetary gear sets.