1. 12 V power supply of the electrical system - when the electric car is switched off and while driving

It goes without saying that a lot of consumers work with 12 V voltage in electric cars as well (e.g. central locking, interior light, tools, etc.). These have been perfected over decades and are used every year in millions of new cars (combustion engines and electric cars). Clearly no e-car manufacturer wants to redevelop them, especially as they don’t consume a lot of power. The 12 V electrical system power supply is therefore also used in electric cars. At the moment, the stability, availability and lower risk mean that a lead-acid battery is used for the 12 V electrical system in all electric cars. This battery for the electrical system does not act as a starter, but supplies the 12 V consumers in the vehicle and thus also supplies the on-board computer, which ultimately controls the high-voltage battery.

2. Safety requires redundancy- when the electric car is switched off

This is because the 12 V back-up battery also serves as a buffer to create redundancy for functional safety aspects. For example, it must be ensured that the steering assistance (power steering) of the electric car continues to function when the engine is switched off so that manoeuvrability is maintained. It is not only in electric cars that the power steering systems of today usually operate electrically.

Furthermore, the driver assist systems are supplied with power from the 12 V back-up battery. The English term “Adaptive Cruise Control (ACC)” has become established in the international automotive industry. Here, the focus is often on safety aspects, but also on increasing driving comfort. Another aspect is the improvement of economic efficiency.

3. High-voltage safety - when the electric car is switched off

Before the high-voltage battery can be accessed, high-voltage safety must be ensured. In order for this to be tested, control units must be in operation. These draw all their energy from the 12 V lead-acid-based electrical system battery.

If the 12 V back-up battery is discharged, the on-board computer cannot start up. If this occurs, the frequency converter is not controlled and starting up is not possible.

4. Carry out staus changes - in the event of failure of the high-voltage system

A second source of energy in the vehicle is necessary to reach the safe state “vehicle stationary” from the safe state "high voltage off". This requires: windscreen wipers, lights, brakes, steering. … this is a basic safety requirement.

All these functions must be guaranteed so that the high-voltage system can be switched off at full speed in the event of an emergency. Many safety-relevant components continue to be supplied with power, for example dipped headlights, audio, autopilot and safety systems, all motors that are not part of the drive - window lifters, windscreen wipers, side mirrors, power steering, seat motors, ...; furthermore brake boosters, interior lights, instrument clusters including main display, power steering and some more.

5. do not jump start with electric car! (BEV Battery Electric Vehicle)

For technical reasons, the jump-start points of electric cars, if any, are not designed to jump-start other vehicles. In this case, it is better to seek the help of a breakdown service. Conversely, however, an internal combustion engine may properly jump-start an electric car.

1. Remove the old battery

You can recognise the electrical system battery by its box shape and the two terminals, which both have a cable connected to them. With newer batteries, the terminals are often coloured red and blue or red and black –– the positive terminal is always marked red.

Banner Tip: 

We recommend, without exception, that before disconnecting and removing the used battery, you use the Banner Memory Saver. This reliably prevents the loss of vehicle data. Through a power supply via the OBD connector (On Board Diagnostic) in the vehicle. 

When the battery is changed, vehicle data such as navigation settings, telephone book, radio station and electric seat position are … retained.

Which terminal do I attach the cable to first –– positive or negative?

Always disconnect the negative terminal first (the earth cable usually hangs onto the negative terminal)! Otherwise, flying sparks or even a short circuit may occur.

Proceed as follows:

• Unscrew the nut from the negative terminal and disconnect the black connecting cable.
• Loosen the nut from the positive terminal to remove the red cable.
• Loosen the screws on the holder system.
• If the battery is now exposed, you can remove it.
• Caution: An electrical system battery weighs between 5 and 15 kilograms. This must be taken into account when replacing the battery.

2. Install the new battery

If you have removed the used battery, you should now properly insert the new one. To do this, insert the new battery into the battery compartment. You should then secure the battery using the holding system and tighten the holding screws. Now you can connect the new battery.

3. Connect the new battery

In order to connect the new battery, it is important that you proceed in reverse order. In keeping with this, first attach the red cable to the positive terminal and tighten the nut. Then fasten the black cable to the negative terminal and tighten nut and screw here as well. Now use the terminal grease or terminal spray –– now’’s the right time!

Additional tip: 

• Replace any existing terminal covers! By doing this, the terminal can be safely covered and protected against short circuits.
• We recommend the use of a degassing tube for all lead-acid batteries which are installed in the interior/glove compartment.
• Some vehicles are provided with a tube, with an attached angle piece, for the discharge of the battery gases. If this applies to your vehicle, the tube shall be inserted via the angle piece into the corresponding degassing opening of the battery. If there is a degassing opening on the other side, it must be closed with a sealing plug!
• Finally, you can replace the battery cover.

4. Close the bonnet after the work is complete

Close the bonnet (or close the boot), open the car and check the electrical system computer display. There shouldn’’t be an error message and you can start the electric car as usual.