The Holden Volt was released in Australia in December 2012. The 2011 Chevrolet Volt has a / 45 A·h ( usable) lithium-ion battery pack that can be charged by plugging the car into a 120-240 VAC residential electrical outlet using the provided SAE J1772-compliant charging cord. No external charging station is required. The Volt is propelled by an electric motor with a peak output of delivering of torque. Capacity of the battery pack was increased to ( usable) for 2013 models, which increased the all-electric range from . Other specifications remained the same. The battery pack capacity was increased to for 2015 models. This incremental upgrade is likely to reflect in an improvement in range over previous model years, but , the 2015 Volt has not been re-certified with the EPA. While driving, after the Volt battery has dropped to a predetermined threshold from full charge, a small naturally aspirated 1.4 L 4-cylinder gasoline fueled internal combustion engine (Opel's Family 0) with approximately , powers a 55 kW generator to extend the Volt's range. The vehicle also has a regenerative braking system. The electrical power from the generator is sent primarily to the electric motor, with the excess going to the batteries, depending on the state of charge (SOC) of the battery pack and the power demanded at the wheels. Prior to the 2016 model year, the Volt required premium gasoline of (R+M)/2 octane rating of 91 or higher because the higher octane permitted the 10.5:1 compression ratio engine to use more ignition timing advance to maximize fuel efficiency by 5 to 10% compared to regular gasoline. For users who drive mostly in electric mode, and to avoid maintenance problems caused by storing the same gasoline in the tank for months, the 2011 Volt has a sealed and pressurized fuel tank to avoid evaporation. As a result, the fuel filler must be depressurized before opening the tank. Also, the 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. The Voltec drivetrain has three power converting elements:  Chevrolet Volt Specifications.doc on the link of the same name. engaged when the batteries reach the predetermined threshold.