engine management system monitors the time since the engine last ran, and prompts the driver to run past the all-electric range before recharging to consume some gasoline. If the driver does not run on gasoline, the system automatically runs the maintenance mode, which starts the engine to consume some of the aging fuel and circulate fluids within the engine. A configuration with an E85 flex-fuel capable engine is under development and was expected to be available in 2013. Operating and driving modes The Voltec drivetrain has three power converting elements: Primary traction electric motor/generator, provides good acceleration for driving at lower speeds and regeneration for braking, its maximum output of 111 kW setting the maximum output of the whole system. Secondary electric motor/generator, works primarily as generator capable of producing 55 kW or when necessary acts as a motor assisting the primary electric motor. Internal combustion engine of 63 kW power, engaged when the batteries reach the predetermined threshold. These units are connected via a planetary gear and three electrically controlled hydraulic clutches to provide power output for propulsion in any of four programmed operating modes: Single-motor electric – The primary motor runs solely on battery power, maximum propulsion power is 111 kW. Dual-motor electric – At higher vehicle speeds the secondary motor engages over the planetary gear such that it reduces the speed of the primary motor. This facilitates higher efficiency and better mileage for the combined system, without increasing the maximum power. Single-motor extended – The battery reaches its minimum charge, which triggers the combustion engine. The engine drives the secondary motor as a generator, via the charging electronics, to keep the minimum battery charge level. The primary motor can still provide its 111 kW for short acceleration, albeit not sustained. Dual-motor extended – The electric motors are used again in dual configuration with increased efficiency at higher speeds. Additionally, the gasoline engine contributes propulsion power via the planetary gear. While power is drained from the battery the amount is less than in mode 2 for the same propulsion power, thus extending the range. The drivetrain permits the Volt to operate as a pure battery electric vehicle until its battery capacity has been depleted to a defined level, at which time it commences to operate as a series hybrid design where the gasoline engine drives the generator, which keeps the battery at minimum level charge and provides power