Battery and charging technology

With its first fully electric series production model, Audi has transformed from a classic automobile manufacturer to a system supplier for mobility. Thanks to a comprehensive range of charging options with intelligent solutions for home and on the move, customers can enjoy fully electric driving without having to compromise.

95 kWh of energy: the high-voltage battery system

The powerful lithium-ion battery in the Audi e-tron provides for a range of more than 400 kilometers (248.5 mi) in the WLTP driving cycle. The battery operates with a nominal voltage of 396 volts and stores 95 kWh of energy. The battery system in the Audi e-tron is located beneath the cabin and is 2.28 meters (7.5 ft) long, 1.63 meters (5.3 ft) wide and 34 centimeters (13.4 in) high. It comprises a total of 36 cell modules in square aluminum housings, each of which is roughly the size of a shoe box. They are arranged on two levels, known as “floors” – a longer lower floor and a shorter upper one. The cell modules in the Audi e-tron can reproducibly discharge and charge electricity over a broad temperature and charge status window. They can be densely packed to achieve a very high output and energy density in the volume available. At market launch, each module is equipped with twelve pouch cells having a flexible outer skin of aluminum-coated polymer. In the future, Audi will use both technically equivalent prismatic cells in its modular concept, also in terms of a multiple supplier strategy.

An indirect cooling system distinct from the cell space ensures the high-performance operation of the battery over the long term. It is made of flat, extruded aluminum sections uniformly divided into tiny chambers. Heat is exchanged between the cells and the cooling system beneath them via a thermally conductive gel pressed beneath each cell module. In what is a particularly efficient solution, the gel evenly transfers the waste heat to the coolant via the battery housing.

The battery and all key parameters, such as charge status, power output and thermal management, are managed by the external battery management controller (BMC). This is located in the occupant cell on the right A-pillar of the Audi e-tron. The BMC communicates with both the controllers of the electric motors and the cell module controllers (CMC), each of which monitors the currents, voltage and temperature of the modules. The battery junction box (BJB), into which the high-voltage relays and fuses are integrated, is the electrical interface to the vehicle. Enclosed in a die-cast aluminum housing, it is located in the front section of the battery system. Data exchange between the BMC, the CMCs and the BJB is via a separate bus system.

Standard with 11 kW, optionally with 22 kW: charging at home

The Audi e-tron will typically be recharged most often at home. And each charging cycle costs the owner just a few seconds of time, i.e. the time required to connect and disconnect the charging cable. In most cases, the electric SUV is charged overnight and then sets off the next morning with a fully charged battery and a range of more than 400 kilometers (248.5 mi) according to the WLTP test cycle.

Audi offers various solutions for charging at home. If desired, an electrician referred by the local Audi dealer will check the power supply in the garage and install the suitable technology. The standard compact mobile charging system can be used in two ways – with a charging power of up to 2.3 kW when connected to a 230 volt household outlet, and with up to 11 kW when connected to a 400 volt three-phase outlet. In the latter case, the battery can be fully recharged in roughly eight and a half hours. The optional connect charging system doubles the charging power to as much as 22 kW. This requires a second charger on board the Audi e-tron, which will be available from 2019. The connect system comprises a control unit with a 5‑inch touch display and a wall mount. It enables customers to view their individual charging statistics and charging progress in the myAudi portal and the myAudi app.

Together with a home energy management system, the connect charging system offers intelligent functions. In this case, the Audi e-tron can be charged with the maximum power available with consideration of other consumers in the household to avoid overloading the electrical system. Customers can also define their own personal priorities, such as charging when electricity is less expensive. If the home is equipped with a photovoltaic system, the car can be charged preferentially using the electricity generated by the system, and charging even considers forecast phases of sunshine.

Remote control via app: charging and heating/cooling

The myAudi app provides for convenient operation with smartphone from the couch. With it, customers can also plan, remotely control and monitor charging processes and the pre-entry climate control of the Audi e-tron. They can set a departure time, for example, so that the electric SUV is charged and/or heated/cooled at the desired time.

Customers can even choose for the first time to heat or cool certain zones in the car. On cold winter days, for example, they can turn on the seat heating, heated steering wheel or the heated rear window using their smartphone. The app also displays charging and driving data. Communication with the car is via the integrated LTE module, which is standard equipment in the Audi e-tron.

At up to 150 kW: charging on the move

Thanks to the long range of more than 400 kilometers (248.5 mi), there generally is no need to stop at a charging station during everyday driving. This is not the case for longer trips, however, such as when going on vacation. In these situations, the Audi e­-tron can recharge with up to 150 kW DC at fast charging stations meeting the European Combined Charging System (CCS) standard – a first for a series-production automobile. This means that the electric SUV is all set for the next long-distance stretch of a journey in approximately half an hour. It is all made possible by the sophisticated thermal management of the lithium-ion battery, which allows charging at up to 150 kW. Plans call for the Ionity network to include 400 such high-power charging (HPC) stations installed at 120-kilometer (74.6 mi) intervals along European highways and main transportation corridors by 2020. The Volkswagen Group including Audi and Porsche, the BMW Group, Daimler AG and the Ford Motor Company are jointly promoting the expansion of the HPC network. Additional compatible HPC charging points are also being installed in Europe outside of this joint venture.

In addition to direct current, the electric SUV can also be charged on the move with alternating current at AC chargers, with up to 11 kW as standard and at 22 kW with the optional second on-board charger. The car is connected to the charging station using the standard mode 3 charging cable. Roughly 95 percent of all existing charging points in Europe currently conform to this standard.

From market launch Audi will offer a proprietary charging service for its customers – the Audi e­-tron Charging Service. It provides convenient access to roughly 80 percent of all charging stations in Europe, corresponding to well over 70,000 public charging points in 16 EU countries. Whether AC or DC charging, 11 kW or 150 kW – a single card is all customers need to start the charging process. Data transfer is based on RFID (Radio Frequency Identification) radio technology. Many charging stations can also be activated by scanning a QR code with a smartphone. To use the service, customers have to register one time on the myAudi portal and conclude a contract. Billing is automatic via the user account. No physical means of payment is used. Customers can use the myAudi portal to view their current charging history at any time, review their latest bills and manage their contract. Independent of this, customers can also use charging stations that are not included in the e-tron Charging Service portfolio. In these cases the customers settle directly with the respective provider.

From 2019 onward, charging will be even more convenient for Audi customers. This is when the Plug & Charge function will be introduced. It enables the Audi e-tron to authenticate itself at charging stations via state-of-the-art cryptographic procedures, after which it is authorized – the card will no longer be necessary. This requires a valid charging contract with the e-tron Charging Service. All Audi e-tron models rolling off the assembly line from mid-2019 will support this function as standard.

In the spotlight: the charging process

Each Audi e-tron charging process begins with a little show: At the push of a button, the motorized charging flap in the driver-side fender opens toward the front to reveal the connector illuminated by a white LED. Next to it is a second LED that indicates the status. A pulsing green light, for example, means charging is active; a steady green light means charging is complete.

When the plug is disconnected, the charging flap closes automatically within five seconds. Together with the optional second charger, Audi provides an additional connector on the passenger side for AC charging.

Important performance factor: thermal management

The effective thermal management system in the Audi e-tron guarantees fast DC charging with up to 150 kW, long battery life and reproducible road performance even under heavy load. For the customer, this means high performance at all times.

The thermal management system of the Audi e-tron comprises four circuits that can be connected in various ways as required. It cools the electric motors including their rotors, the power electronics and the charger. It also cools and warms both the interior and the high-voltage battery. The rotors, which reach up to 13,300 revolutions per minute during real vehicle operation, consist of magnetically conductive electrical sheets and lightweight, high-purity aluminum. Coolant flows through the inside of the shafts to ensure that the temperature does not exceed 180 degrees Celsius. The stators and end shields of the electric motors are also water-cooled. The gearboxes mounted on the end shields benefit indirectly from this solution. Effective cooling posed new challenges for the developers, particularly with the coaxially arranged electric motor at the rear axle. The solution is to supply the coolant via a double-wall pipe and its ceramic seal on the electric motor rotor.

22 liters (5.8 US gal) of coolant circulate around the 40 meters (131.2 ft) of cooling pipes in the Audi e-tron. Being the hottest components in the powertrain, the electric motors provide the thermal management system with a large quantity of heat. The standard heat pump uses their waste heat – up to 3 kW of actual power losses are efficiently used for heating and air conditioning the interior. Depending on the outside temperature, that can boost the Audi e-tron’s range by up to ten percent in customer operation. 

The thermal management system also ensures that the battery is kept within its optimal efficiency range of 25 to 35 degrees Celsius in all situations, from a cold start in winter to fast highway driving on hot summer days. This also contributes to the long service life. During DC charging with 150 kW, which is possible for the first time ever in a series production automobile with the Audi e-tron, cold coolant dissipates the heat produced as a result of electrical resistance. If the battery is still cold when charging in winter, it is heated with warm coolant.